The Greatest Stage (One Piece/Warhammer 40k) (Second Primarch SI)

“Guys! Wait up! Wait for me!” Luffy cried out, running as fast as he could after his brothers. Both of their backs were far ahead of him, easily jumping from branch to branch or leaping over massive tree roots. Both of them wielded pipes, similar to the one that was strapped to his back, clearing a path for him, but even then, he saw that they were moving further ahead. 

Sabo glanced over his shoulder, grabbing onto his top hat to make sure it didn't fly off. “We can't, Luffy! We gotta get there first!” He called out, sounding sorry. Unlike Ace, who didn't even turn around. 

Luffy's gaze went up, spying a thick column of smoke that still lingered in the air. They had been on their way to the Gray Terminal, a humongous garbage dump outside of Goa city, when they saw a huge rock falling from the sky. But they hadn't been the only ones, so it became a big race to reach whoever the rock fell first. They had the lead because most of the adults couldn't make it through Midway Forest without getting eaten by a tiger or monkey. But some still remained in the race. 

“But…” he started to whine before an idea struck him. Sabo saw the grin, and he looked worried-- he didn't need to be. This was gonna work great! Now, he just needed a name… “Gum Gum…” He started before flinging his arms forward, and they stretched like rubber, his hands grabbing his own forearms as he wrapped them around a pair of tree trunks. Skidding to a halt, he started running backwards. 

“Wait, Luffy, that's a terrible idea-” 

“ROCKET!” Luffy exclaimed, hopping up and letting his arms slingshot forward. He blitzed past Sabo and Ace, the latter letting out a yelp of surprise when he shot forward overhead. It didn't take Luffy more than a second to figure out what Sabo meant when his face was peeled back from the speed and the branches he crashed through whipped at it. “AAAAAHHHHHH! ACE! SABO! HELP!” He yelled, speeding through the branches until he cleared them entirely. 

He got a glimpse of their destination before he started to fall. There was a really big crater, and around it were a bunch of trees that got knocked over. His limbs flailed for something to grab onto, but found nothing. He landed face-first at the edge of the crater before rolling all the way down to the center where his face struck the thing that fell from the sky. After unflattening his face, Luffy blinked a few times now that he got a real look at it. 

“... Two?” He read, seeing the number written on the metal surface. Getting up and dusting himself off,  he stood up and looked past the dust and the scorched surface to see that it wasn't a rock at all. It was a casket. A metal one. 

“Luffy!” He heard Ace call out, his tone worried and furious as he was the second to arrive. Without wasting a second, he slammed a fist down on his head hard enough that his neck stretched and he hit the casket again. “You scared the hell out of me! How many times do I havta’ tell you to… huh?” Ace started, getting distracted by the casket too. 

Luffy's head snapped back to his shoulders and he patted Shank's strawhat to make sure that it was okay. Then he grinned at Ace, “I was here first! I beat you, Ace!” He said with a laugh, making his brother scowl as Sabo arrived. 

“You sure did, Luffy. That was a clever use of your Devil Fruit power,” he praised and that made Luffy smile broadly. 

“Tsk. Enough of that -- what's this thing? I thought it'd be some cool space metal, but it looks like normal steel. Lame,” he added, giving the casket a kick. 

“Whatdaya mean lame?” Luffy protested, pointing at it. “It fell from the sky! It's… a sky treasure!” He said, pointing at it. And, as if to agree with him, the casket suddenly let out a hiss of air that scared all three of them. But they reacted by grabbing their leap pipe staffs and leveling them at the casket, ready to beat the stuffing out of anything that came out of it. But, through a haze of steam, the three of them gaped at what was revealed when the door of the casket slid up. 

It was a baby. A really big one, almost as big as Luffy was, and he was seven. His hair was black and his eyes were butterflying open, revealing eyes that were a red amber color. It took him a minute to fully open them before the baby shifted, looking around before his eyes fell on them. 

Luffy instantly looked to his brothers, “W-what do we do? It's a baby! A baby fell from the sky!” He exclaimed, and to his immense horror, his brothers looked as clueless as he did. 

“I dunno?! I didn't think there would be a baby in there! Can't we just leave it and take the- ow!” Ace shouted, rubbing the back of his head where Sabo whacked him with his staff. 

“We can't just abandon a baby, idiot! It's a baby! What if someone like Bluejam finds him?” He asked, making Ace wince in a way that didn't come from the goose egg on the back of his head. 

“So, we take him with us?” Luffy asked, looking back at the baby to find that he was looking at his hands with astonishment. “But I dunno anything about babies? Do you think Dadan would?” 

Ace scoffed, “She's a mountain bandit.” He answered, and that's all he needed to say. 

“Then Makino?” Luffy tried, and Sabo gave him a surprised glance. 

“That's… actually a good idea, Luffy,” he praised him, making Luffy puff out his chest.

“Thank- wait, whatdaya mean, ‘actually’?!” He shouted, earning an apologetic laugh from his brothers before he pouted. “I can carry the baby if you guys can get the thingy,” he said, his arms stretching out and wrapping around the baby that was as big as he was. The baby seemed a little surprised, but he wasn’t crying or anything. Luffy gave him a friendly smile as he put him on his back, and the baby wasted no time pinching and pulling his cheek with a sense of wonder. 

“Yeah, sure, but do you even know the way to Foosha Village?” Ace asked, making Luffy think about it for a few seconds. And then he laughed unapologetically, meeting Ace’s flat stare. “Not even a clue, huh? Fine. Whatever. We’ll go to Dadan first -- she should at least be good to give us directions.” He said, glancing at Sabo and earning a nod. Then the two of them grabbed hold of the casket and lifted it up with ease. It was pretty big, but it wasn’t alligator big. 

“Let's get out of here before the others arrive. They shouldn’t be too far behind by this point. We’ll have to take the long way back,” Sabo said, earning a pair of nods before they took off back into the forest. They snickered when they heard shouts of despair in the distance when the adults arrived, only to find nothing. 

The long way back to Dadan's was a winding path -- they had to jump over gator-infested rivers, sneak around battle baboon territory, cross the chasm that belonged to the direwolves, and a whole bunch of other stuff. But, within the hour, they managed to find their way to the convoluted path up Mt. Colubo to the small house that belonged to the mountain bandits. While Ace and Sabo were setting down the casket, Luffy pushed open the front door. 

“Guess what we found?” He announced himself to the bandit tribe within. He hated mountain bandits, but Dadan and her tribe were okay. They were all hunched over a fire, having a conversation about who to rob or something, before perking up to look at him. 

Dadan was an old hag with red hair and a cigarette dangling from her lips, and her eyes went wide the moment that she saw them. “Is that- did you kidnap a baby!? Please tell me that you at least kidnapped one worth ransoming back…”

“Wha? No way! This… this is my new little brother!” Luffy decided, his face brightening as he set down his little brother down. He was looking around at the interior of the building, not seeming too impressed with what he saw. That changed when one of the mountain bandits stepped out carrying a plate full of meat. His stomach growled at the smell, but he turned to Ace and Sabo as they entered. “You hear that? He’s our little brother now. Our. Little. Brother.”

“As if, Luffy,” Ace shot back with a teasing smile. “You’re always going to be the baby brother. Plus, he’s like one growth spurt away from being bigger than you.”

Luffy’s expression twisted, “No! I’m a big brother too now!” He shot back, glowering at Ace, who met his glare head on. But, unlike usual, Sabo didn’t interfere to defuse the argument before it could really begin. Sneaking a glance from the corner of his eye, because he really didn’t want to get beaten up by Ace, he saw Sabo gaping at something behind him. Luffy whipped his head around and-

“Ah! The meat!” He gasped, tears blurring his vision as he saw the empty plate on the ground and the baby lying next to it with a bulging stomach. He burped in contentment and promptly fell asleep, unconcerned with the betrayal. 

Off to the side, Dadan was rubbing her temples as a vein throbbed in her forehead. “Is there not a single normal child on this damned island?” She growled before glaring in their direction, “Well? You going to explain how you ended up with a giant infant or what?”

Ace shot her a sullen look, “He fell from the sky. We took his pod with us -- it’s outside.” At that, her eyes widened and she rushed outside, sticking her head out the doorframe to see the scorched pod. The cigarette fell from her lips because when she jerked her head back inside, it was missing. 

“And your first thought was to bring him here?!” She shouted at them, making Ace scoff. 

“No. We were gonna bring her to Makino, but Luffy doesn’t know the way,” he answered, making Dadan drag a hand down her face. The other mountain bandits weren’t much better, clamoring outside to look at the casket and talking amongst each other about how much it would sell for. “But, since we’re here -- you know anything about babies?”

“No! Why would I? I wouldn’t even want you brats here if it weren’t for Garp!” She shouted, and Luffy laughed. She wasn’t very honest. She wanted them here, but she had to look tough when everyone already knew she wasn’t. “I especially don’t know what to do with babies that fall from the sky and eat ten times their weight in meat!”

“I was just asking. Sheesh,” Ace muttered sourly, rolling his eyes before they landed on the baby. Then they narrowed, “Luffy?”

“Yeah?” Luffy said, looking at Ace, who was tilting his head at the baby.

“Does he… look bigger to you?” He asked, making Luffy look over. He narrowed his eyes before walking over, peering at the slumbering baby. Then he walked circles around him. Then he laid down next to him to check their- “Ha!” Ace laughed when Luffy’s expression twisted, “He’s already bigger than you, Luffy!”

“Shut up, Ace! He… He’s going to be bigger than you, too, you… dummy!” He shouted back at him, while Sabo frowned at them both. 

“Guys -- it’s not normal for a baby to grow… half a foot in a few hours,” Sabo pointed out. 

Ace shrugged, “It’s not normal for ‘em to fall from the sky either.” To that point, Sabo nodded his head. “You think there’s something wrong with him? He’s not sick or anything, right?” He added, a touch of concern in his voice, while Sabo walked over, kneeling on the other side of the baby and placed a hand on his forehead. 

And then their little brother opened his eyes as a loud yawn ripped from his throat, “What a weird dream.”

“... huh?” Luffy muttered while the others stared on in shock, their jaws dropping until they hit the floor. The noise drew their little brother’s attention to him, and his amber eyes met Luffy’s black. Luffy saw confusion fill them as incomprehension dawned on his face. 

“Eh?” His brother muttered back at him. 

“Huh?!” 

“Wha?!”

What was going on?!

[center]…[/center]

‘What’s going on?!’ I thought, finding myself utterly gobsmacked as I looked at a young Monkey D. Luffy’s stupefied expression, openly gaping down at me with his signature strawhat resting on top of his head. I thought it had just been a really weird dream, because what else could it be -- I woke up in the body of a literal infant that crashlanded in some kind of pod. Like, there was no way that wasn’t a dream, so I fully expected to be back in my old body upon waking up. 

Only, I hadn’t. I was still here. In One Piece.

Honestly, I really wished I had gotten a ROB introduction or something, because at least then I could have braced myself for the gut punch of getting Isekai’d for seemingly no discernible reason. Unless I had died in my sleep, I… no, I didn’t even want to think about that for now. There would be time for it later. Right now, I needed to focus on the fact that Monkey D. Luffy, the protagonist of One Piece, was staring down at me with utter bewilderment. 

He was a kid. And, looking over, I saw both Ace and Sabo, telling me that I was pretty early on in the timeline. Not sure if that was a good thing or not, considering that the world went to hell in a handbasket in a few years with Luffy at the epicenter of it all. Being younger than him didn’t exactly bode well for my ability to prepare for the endless slew of bullshit that was coming.

And it was then that I noticed something really strange. 

I had made that thought in a fraction of a second. Luffy hadn’t even blinked his eyes yet. My brain felt… weird. Weird in a good way. The only thing that I could possibly compare it to was putting on a pair of glasses for the first time and realizing how blind you had been up to that moment. Every thought came fast. Sharp. More than that, even as I was thinking how utterly insane me being here was, I was also thinking about how I was able to think better. Just as I was noting the details of Luffy’s attire and guesstimating my place in canon. Simultaneously.

I was thinking entirely separate trains of thought all at the same time. It was pretty weird. 

“You can talk!?” Luffy shouted, staggering back with wide eyes. He wasn’t speaking English. It sounded a bit like Japanese but… huh. 

I’d… just figured out how to speak Japanese. Crystal clear memories of watching anime and reading subtitles, coupled with a handful of interviews, gave me all the context I needed to learn the language. More than that, I realized that I’d figured out whatever language Luffy was speaking because I had heard it while I was asleep, and I just… figured it out. No lesson plan or anything. Just hearing a few words and working out how the rest of the language would work in the span of like, three seconds. If that.

So, on the bright side, I seemed to have gotten my overpowered isekai ability. That’s nice, I guess. 

“Yeah?” I replied, sitting up and once more looking down at my hands. They were still small, but they weren’t quite as infantile as they had been mere hours ago. More importantly, I had perfect control over them. There was no baby clumsiness to be found in me. I didn’t struggle for balance when I stood up for the first time- it was the opposite. My balance was perfect. I’m not sure if I could fall over even if I was trying to. 

“One child. Is there not one normal child?” Dadan breathed, massaging her forehead. I glanced in her direction, noting the stress lines that seemed to deepen by the second. Then she leveled a look at me, “So, you feel like explaining why you came crashing down to earth?”

“... I’m a literal newborn baby. Why would I know?” I asked, playing off my ignorance, but I had to admit that was a really good question. I was clad in a little bodysuit which hadn't seemed to grow any tighter with my growth spurt, and it didn’t feel like any material I was familiar with beyond it feeling like a weird mix between silk and polyester. “Can I see my ship?” 

I was looking at Luffy, Ace, and Sabo -- none of them seemed like they had any idea how to handle the situation, but they all seemed to collectively shrug that off. Ace offered a nod, “Yeah, it’s outside. So, are you like… an alien or something?” He asked, sounding curious and poking me with his staff as I walked by him. 

“I don’t think sooo…” I trailed off, seeing my pod and, more importantly -- the ‘II’ that was etched into the base of it. My mind lurched in a certain direction, but it was when I stepped forward and brushed off the soot with a hand that I confirmed it. A double headed eagle. 

The symbol of the Empire of Mankind. 

Meaning that this was a One Piece and Warhammer 40k crossover. That sounded… frankly pretty absurd, if I was being perfectly honest. Really crossing the streams there. Warhammer 40k was about a galaxy perpetually at war where everyone sucked, there were no good guys, and things would never get better. One Piece, on the other hand, was a more lighthearted tale where you could punch evil in the face and make the world better with every blow. 

It did explain a few things about myself, though. If I was right, and I almost certainly was, then the II on the pod represented the Second Primarch. Which was me. Not sure if that was a good thing, considering that the Second and Eleventh Primarchs were expunged from history. So, did the Emperor of Mankind take one look at the original Second Primarch and write him off the second he saw whatever he got up to in One Piece? Or had he landed elsewhere and this start was just for me? 

I'm not sure which idea worried me more, frankly. 

The information left me feeling uncertain. Just for a moment. Being a Primarch came with some expectations -- like genociding the xenos, conquering human civilizations that resisted the boot heel of the Imperium, and of course bowing my head to the Emperor of Mankind. My ‘father’, in the loosest sense of the word, whose record was spotty at best when it came to dealing with his kids. The Grand Crusade would last some two hundred years, and in that time, untold trillions would die across the galaxy in the name of unity. 

But my hesitation only lasted a moment as Luffy was quick to grab hold of me, “So… you're an alien, right? I have an alien for a little brother, right!?” He asked, but his tone told me that there was a correct answer to the question. 

“I su-” I began before pausing. Then, in a different cadence, I continued. “I am an alien, I suppose~.” I did my best to sound like an alien, and there were stars shining in Luffy’s eyes. 

Then he started crying, “I… have an alien brother… It’s so cooool!” He hiccuped and I snorted. Luffy grew older, but he never grew up, huh? Well, that wasn’t a bad thing, I don’t think. I had been up to date with the manga by the time of my isekai, and things had worked out pretty well for him. And that in itself was its own can of worms -- though, thinking about it, the World Government and the Celestial Dragons would fit right at home with the Imperium of Mankind. The 40k version, even. 

“So, what now? I kinda figured… I dunno, that’d we havta’ raise you or something,” Ace spoke up, tilting his head at me like he couldn’t figure me out. Given what I was, that was a fair reaction. In their eyes, they’d found me as a baby like an hour ago, and now I was walking and talking. “Did your alien dad give you a name at least?”

“I don’t know. I don’t remember anything about my parents. Or why I was in the ship,” I fibbed, but only a little. I knew what I knew because I had been on a 40k lore kick because of the Rogue Trader CRPG. I didn’t personally remember a thing about the Emperor of Mankind, or anything about the journey itself. As for my name… couldn’t lie, it was just plainly a little underwhelming for a Primarch. 

“We get to name you? Then your name should be… hmmm… hmmm,” Luffy began with obvious excitement, only to trail off as his expression became one of intense concentration. He was really putting those two brain cells to work.

“It’s gotta be a cool name. We can’t have a brother with a lame one,” Ace voiced, crossing his arms and puffing out his chest. Wouldn’t hear any arguments from me there.

Sabo perked up, “What about Edward? There was a Goa king named that, and he was pretty cool-”

“Rayleigh!” Luffy blurted, catching the others by surprise. “Shanks talked about a really cool old guy who taught him how to be a pirate, and his name was Rayleigh! I almost forgot! Shishishishi!” Ace’s expression immediately began to twist, but whatever he had been about to protest with was swallowed down. Luffy didn’t wait for their input either, simply reaching out and rubbing my head, “Your name is Rayleigh now, okay?”

I gave it a moment of thought before I nodded, “Rayleigh. I like it,” I said, making Luffy brighten immeasurably. Sabo was patting Ace on the back, who just shook his head to dismiss his reservations. 

“Fine. But you’re taking my last name, got it? Portgas!” Ace warned, raising a fist to bully me into acceptance. He seemed genuinely stunned when I simply nodded. It was actually a little sad to see, if I’m being perfectly honest. Ace was a little bundle of neuroses and insecurities, and any acceptance seemed entirely unexpected by him. 

“What about me?” Sabo pouted, making Ace snicker. 

“You wanna give him your last name?” He asked, elbowing his brother, and Sabo responded by giving some serious stink eye before delivering a kick to the shin. Ace just cackled. But, tellingly, Sabo didn’t argue the point. “Portgas Rayleigh. Kinda a mouth full, but it’s good enough for me.” Largely, I imagine, because he gave me his last name. 

I watched the entire interaction happen, feeling warmth in my chest at the open acceptance and adoption into the family. It felt nice. Far more so than I anticipated. All the more so when Luffy lowered his hand and looked to the others. 

“We gotta share another cup of sake- that way we’ll really be brothers,” Luffy pointed out, and it was then that Dadan reentered the picture, looming over the four of us like a giant. 

“Sake?” She echoed, making Luffy start sweating bullets. “Where did you brats get your hands on sake?”

“We raided your stash-” Ace informed unrepentantly, laughing when she took a swipe at him and the three brothers took off. I was nearly left behind until Luffy stretched back his arm to grab my hand to drag me along with them, all the while Dadan shouted at our backs and swearing a bloody vengeance. 

Luffy smiled at me over his shoulder, “Don’t worry about her, Ray -- she’s actually super nice. She just acts like a mean old hag,” he said, making Ace snort from ahead of us. 

I was able to keep up with them. The fact kinda of surprised me. Ace, Sabo, and Luffy were children who beat the shit out of hundred-ton monster animals on the daily because that was the closest thing they had to entertainment. I wasn’t too knowledgeable on the whole power scaling thing, but I’d kinda expected them to leave me in the dust, even as children. But, I found that I was easily able to keep pace with them. 

Every movement felt impossibly smooth, my body responding to my brain in ways that my old body just couldn’t have managed. I followed behind Ace, copying his movements perfectly as he hopped from root to root, swung on a vine, or even jumped off the backs of gators that slumbered in a pond. It was like I had been living all my life with this little bit of lag that I’d only noticed once it was gone. 

It was the same for my senses. I couldn’t just smell scents in the air; I could taste them. I could see in incredible detail without the need to focus on anything in particular -- I could see the individual droplets of water that made the morning mist in the air, the fine hairs of an insect as it crawled along a leaf, the rivets and grooves of the trees around us. The slightest sounds from what felt like a mile away echoed in my ears. It was almost overwhelming. It should have been overwhelming. Yet, it wasn’t. 

The Emperor did good work, I realized. My brain was designed around all that extra sensory data, so the only apprehension I felt about it stemmed from the fact that I was comparing it to my old senses. I might as well have been blind, deaf, and dumb in comparison. Honestly -- the whole transhuman elitism of the Primarchs and Astartes made a lot more sense to me now. It felt like a genuine insult to compare my new body to my old one; the difference was that stark.  

“Wouldya’ look at that? He’s already doing better than you did, Luffy!” Ace called out, his tone teasing. 

“Rayleigh! Slow down and wait for me! You gotta listen because I’m your older brother!” Luffy shouted, seemingly incredibly annoyed that he was still bringing up the rear. “Little brothers obey the older brothers!”

Sabo threw back his head and laughed, “Since when have you ever done anything that we said?” He threw back, making Luffy look away, knowing that was entirely too true. 

But he was saved from having to argue as we arrived at our destination. I recognized it from the anime, though it had undersold how expansive it was. The tree itself was utterly massive, standing at hundreds of feet tall, if not thousands. The boys had woven a tree house up the trunk with stairs connecting rooms that were divided by the branches. It looked like an absolute death trap with crooked boards and mismatching paint, but it was impressive all the same. 

“That's our house! We built it,” Luffy informed proudly. 

“We'll need to grab another blanket and pillow,” Sabo noted as we walked to the spiraling staircase that wrapped around the trunk of the tree. 

Ace grunted, “Should have robbed the bandits. Shoulda grabbed the space ship too. That lot will sell it off the moment they figure out how to lift the thing.” Then he cast me a sideways glance, “You got any attachment to that thing?” 

I gave it a moment of thought before I shook my head. I'd have to check the pod over, but I doubted there would be something especially useful on it like an STC or a message from the Emperor. From what I understood, it was just a gestation tank that got tossed into the Warp and crash landed here. There would be some interesting technology, I would imagine, but nothing that would be too relevant to me. “You're going to sell it?” 

To that, Ace glanced at Sabo, who offered a small shrug. “I might be able to find someone at the auction house to buy it. Nobles love novelty kind of stuff, so we'd probably get a good price for it. And if we can't, then… well, it managed to survive an impact like that, so it's gotta be pretty tough. We could scrap it.” That seemed like a bit of a loss, but no skin off my nose.

“Hm. I'm going to grab the sake. Take ‘em to the spot,” Ace instructed before Luffy started tugging at my hand. 

“It's the same spot where we became brothers- ah!” Luffy started before he seemed to catch himself. He coughed into a fist before making an attempt to sound dignified, “It's a super sacred ritual. People who drink sake together become brothers,” he elaborated, thinking me ignorant. The contrast between his attempt to sound older and wiser with his own nature got a smile out of me as he and Sabo took me to a clearing nearby. 

I saw the stump where the three of them became brothers in the manga, and I took a seat at it. Ace arrived not long after with a bottle and four cups, though one of them was a converted bowl. It felt a bit fitting, I thought as Ace started pouring the sake in the glasses. I got the odd one out. 

It felt like I was intersecting myself into something. Wrongfully so. In perfect clarity, I could recall every page of the manga and every second of the anime. I hadn't witnessed them in this life, but I recalled them all the same. I knew the trajectories of their lives, and seeing the tree house… I also knew what was coming. 

Sabo would be separated and presumed dead by the two brothers after the burning of Gray Terminal, seemingly killed by a Celestial Dragon. Only to still be alive, just with total amnesia, living out his life ignorant of who he was in the Revolutionary Army. He would only learn what he lost when it was too late. 

Ace would go on to become an infamous pirate and the eventual Second Division Commander of the Whitebeard Pirates. When Blackbeard killed a fellow crewmate for a Devil Fruit, Ace would take off in a quest for vengeance, which would lead to his defeat and capture by the Marines. There, at Marineford, Ace would die -- not by execution, but to save Luffy when Ace took the bait of Akainu trash talking Whitebeard. 

Luffy was the protagonist of the story. In two years, he would take the world by storm. Going from a no name pirate to a member of the Worst Generation in the span of a year. He would suffer a grievous defeat, both at Sabaody Archipelago and Marineford, where he would be separated from his crew and then fail to save Ace despite herculean effort. Then he would go to ground and train relentlessly for a period of two years before coming back stronger than ever. In the year following his return, Luffy felled two Emperors of the Sea and became one himself while racing towards the final showdown that would decide who became King of the Pirates. 

I felt like an interloper as I glanced down at my reflection in the cracked ceramic bowl, looking at a face that didn't feel like mine. Because my mere presence had irrevocably changed things for them, and not in ways that were wholly good. I could avoid the circumstances that led to Sabo nearly dying and losing his memories. I might be able to save Ace at Marineford, should a thing still happen. 

But I was a Primarch, created to be a tool of war by the Emperor of Mankind. I was lost for now, but eventually I would be found. One day, he would arrive at this planet to reclaim his weapon of war so that I could lead my Legion to scour the galaxy of any would-be threat to human supremacy, and the galaxy was filled with nothing but threats. I didn't have all the answers at the moment, or even a fraction of them -- but I did know this. 

On the assumption that I’d arrived on this planet within the year that I and my fellow Primarchs were stolen and scattered by the forces of Chaos… I had at most twenty-nine years before the Emperor's arrival. And when I thought of the crazy and chaotic world of One Piece -- one with fish-men, Minks, giants, and so many others the Emperor would label as abhuman… 

What would he think when he looked upon the power of Devil Fruits? Would he see their value and power? Or would he scorn them, seeing them as a product of the Warp? 

I didn't know. There was very little known about the original Second and Eleventh Primarchs, only that their existence had been expunged from history. The fact that they were so successful in doing so meant that the Primarchs had been a small enough problem that their existence had been able to be swept under the rug. And that was frightening to consider. It felt like an executioner’s blade was looming overhead, that my presence had invited a disaster that this world wouldn't be able to survive. It couldn't. Not with the forces that the Emperor could bring to bear. Not when he could throw a Cyclonic Torpedo at the planet to scour it of all life.

“Rayleigh!” Ace began, holding a cup aloft as a wide grin tugged at his lips. “You're a pretty weird guy, but that should be expected since you're an alien. But, you can't be any more troublesome than Luffy.” 

Luffy immediately protested and I looked up from my reflection. Sabo, however, was grinning my way. “We're a wild bunch,” he admitted freely with open acceptance. “We fight, steal, and train every day. So one day we can become pirates -- the most infamous ones that ever sailed the seas! There won't be a day of peace to be found, because Luffy will always find trouble.” 

“You guys are being mean!” Luffy protested, making Sabo raise an eyebrow. It got a laugh out of Luffy, “Yeah, you're right, though.” At least he was aware of it. He followed Ace's example and held up his cup of sake. “I will no longer be the youngest brother! I'll get to do big brother stuff, like showing you all the tasty berries and sometimes I'll even share some meat with you. I'll show you how to fight too, so one day we can even beat up grandpa!” 

There was an unapologetic earnestness in Luffy's words, regardless of how scatterbrained the proclamation was. All the more so when he breathed in and exclaimed, “Because I'm going to be the King of the Pirates!” 

“Heh. And I'm going to be the most infamous pirate that ever lived,” Ace followed. 

Sabo held his own cup aloft, “I want to have a lifetime of adventures and see everything in the world, so I can write stories about it all!” 

The three of them turned their gazes to me, and there was a part of me that wanted to refuse. Not because I wasn't touched by the natural acceptance that they offered -- they had known me for all of a few hours, and they’d just… decided that I was part of the family. No, that part of me wanted to refuse because it felt dishonest. 

My existence was a disaster for them, and they didn't even know it. Their dreams and lives could be cut short by the Emperor's arrival if he found it too dangerous to allow integration. 

I looked down at my cup, thinking a thousand things in the long second that I hesitated to raise my glass. Plans and ideas were formed in nanoseconds, only to be discarded by the next. All of it was painting a single path forward -- knowing what I knew of the Emperor… 

The Great Crusade, which lasted two hundred years, was a mad rush across the galaxy. Speed over precision in galactic conquest -- the Emperor acted like a man racing against a clock, which explained his many decisions that were beneficial in the short term but disastrous in the long one. That was something I could use. As was something else. 

The Emperor granted his sons who managed to conquer the planets they arrived on greater leeway than those who failed to. He’d also granted Ultramar, Roboute Guilliman's budding empire, more freedoms as it was easier to integrate it than it would be to conquer it.

That was the needle I had to thread.

“I want to conquer the planet and build a ship to sail the stars,” I said, raising my own glass. It wasn't a dream. Not really. It was a desire, though. A necessary sacrifice to prevent their dreams from being cut short. 

I had to conquer this planet and create an interstellar empire strong enough that the Emperor decided that we weren't worth fighting, and not so strong that he decided to cut a potential headache in the bud. All of it done within twenty-nine years at the most generous estimate. 

There was no judgment in their eyes as I said the words, just dry amusement in Sabo's eyes while Luffy laughed. Ace just snorted, “Yeah, that sounds like the kinda dream an alien would have,” he said as the four of us clashed our drinks together in a toast. 

The sake tasted absolutely awful, but I didn't mind. 

I couldn't, when it gave me three new brothers. 

…

I’ve been on a bit of a Warhammer 40k kick lately, and I got all caught up on One Piece. At the worst possible time, too, since I got left on a cliffhanger. But this is the result of the dual binge, and despite feeling like very different types of stories, and they are, they mesh surprisingly well in some areas. I have to finagle the connection a bit, but I can make the connection to stuff like the Warp or whatever Imu’s whole deal is. 

To that end, I’ll be upfront with the fact that the One Piece side of the story will not be canon-compliant. I can only guess at some of the answers to long-established questions Oda has been cooking up for two decades, so some of them I’m going to make clear 40k-inspired answers. 

An example would be the Void Century, so spoilers if you aren’t caught up to Egghead Island. While I have absolutely no idea what went on during the time period, I’m going to make the leap of logic that the reason why there was a super advanced society that got ganked by the proto-World Government was that they found parts of an STC. Or that Devil Fruits are basically a warp connection that people can eat.

For this story, I see One Piece as the opening act, but I would say we would have a decent stay in the setting. However, I will be moving through the early game fairly quickly. And by quickly, I mean by chapter ten, the plan is to be in the New World. I’m not sure how long the One Piece stay would last, but I plan to do a few small arcs to cover Ray’s conquest of the planet and how he integrates the One Pieceness elements into his interstellar empire. 

Stuff like his anti-Alpharius spy agency will be Cipher Pol, or exploring how to utilize Devil Fruits like the Door-Door fruit or Mirror-Mirror to create a planetary or possibly interplanetary teleportation network. Or experimenting with how Devil Fruits, especially Awakened versions, change the tactics of warfare when you can low-tier reality warp the ground underneath the enemy into strings. Or creating a science dream team around Dr. Vegapunk and giving them Devil Fruits like the Op-Op, Sick-Sick, Munch-Munch, or Gas-Gas Fruits to facilitate their experiments and tech development. 

As for the 40k side of things -- what I’m looking to cover is the Great Crusade, meeting Ray’s twenty other siblings, including the 11th Primarch, and the Heresy. Even if it might not necessarily be Horus’ Heresy. The plan is to break from canon pretty early on, so other Primarchs would be found earlier; some would avoid their fall, while others might fall in their stead. To that end, I would say it would be something of the more standard Primarch SI about exploring the changes made to canon and the ocean of lore of the setting. 

Also, since it’s a subject of debate, the version of the Emperor I’m intending to use is one that is trying to safety-proof the future he’s trying to reach, but he’s fueled by spite for Chaos and ‘Fuck it, we ball’ energy. So, that’s going to be fun. 

Despite being a pretty weird crossover, this story feels like it has a lot of potential, so let me know what you think.