"the highly anticipated never before seen book from an artist I didn't know did H stuff"
Basically Ikeno himself. This dude draws hentai and beastiality. Nekomusume is just an extension of his fetishes.
@Chizan I'm not 100% sure, but I think those characters come from the books he sells at Comiket. His doujin circle is called AltitudeAttitude and the characters come from a book called "Ayakashippoi" or "Ayakashi-like" which reminds, me I need to add in a translator note.... (thanks! lol)
@Chizan There's a vampire girl in the back left of page 6 who is from Ike's non-h contribution to the hentai magazine Towako (volume 2). That chapter also actually has a cameo of Jorougumo and Kucchi from this series.
The page in question, with both the vampire girl and the cameo: https://i.imgur.com/mqLOZ37.jpg