I'm a bit late to this one, but I didn't see people touching on this in the YT comments, so...
It was pretty fun watching your reaction to the Nezuko-head-kick lmao.
Yeah, we use phrases like 'it's in your blood' or 'bloodline/pedigree' for skills and traits in English!
Cellular Reproduction is as old as hunger, though sexual reproduction is newer, as far as I remember.
Regarding Tanjiro's stamina- worth noting that he traveled through a night, stopped to make a basket before traveling through the day, and didn't get to stop or sleep a second night due to the demon encounter. He then ran all day while following Urokodaki. Then spent another night running down a mountain!
Please continue dissecting demon lore/biology/traits as well as the brother/sister relationship, etc. Your brain is so interesting, and it's always fun when you help me realize something I hadn't on my own watch. :)