This series is created and illustrated by Haruki. He's done a lot of erotic manga and this is one of his longest running, along with Sense.
The plot is maybe half a cut above hentai level, most of it just an excuse to get our heroines into as many tentacular situations as possible. No complaints here.
His works feature girls with very pretty faces and bodies that are heavily influenced to look like real female bodies from the Japanese Adult Video industry. Very few artists can match his ability to draw squeezable looking breasts.
This series is currently at 11 volumes, with 8 of them being available at public download sites. Thankfully those rips are in fair to good quality.
I went ahead and bought volumes 9-11 on ebook and had them ripped too. You never really know what kind of quality you'll get from ebook, it can range from average to top tier. Thankfully in this case the ebooks images were of extremely good quality.