there's very few hentai that go longer than one volume. in fact, most of these are single stories. there's nothing more to add anyway. endless orgies with the same characters would get boring. also, pei is regularly releasing via comic kairakuten beast (and did via comic grape too if the still does).
@Galder
Do you read chapter 9? The story in chapter 9 doesn't seem to end properly yet. If this doesn't get axed then why the author introduce a new character at the end? This is erotic manga, not horror manga. What about camping plan? Are you still plan to tell me that "there is nothing to add"?
@ishtarclover many hentai manga have store exclusive booklets and/or limited editions (for toranoana, melon books or any other hentai retailer). in some of these certain side characters are part of the action. so she might be either starring in one of the extras or is a nod to an older work. some hentai artists feature characters in several books.
the same goes for their training camp. there could be a 4 or 8 page store-exclusive short booklet showing them fucking there. point is, most hentai manga end after one volume.
(Thanks to @arizaga for the lead.)
According to dlsite[dot]com (product_id/BJ150576.html), it has at least 20 chapters that are published as chapter unit. So @SquigglesJP, please remove the `END` label in chapter 9. It cause misunderstanding. Thanks.
P/M: It seems like DLsite even offer a full color version. Also, chapter 9 we got here seems like a omake for vol 1 only.