We previously published here that the author of the Kiss x Sis manga had sold an adult doujin from his series on Comiket 100. According to the author himself, this doujin has adult sketches of the Kiss x Sis characters that he made.
So he decided to create this little doujin and sell it to show all the fans the sketches he had done.
I can’t put the images here as they are explicit despite being unfinished drafts, but you can check out the adult Kiss x Sis doujin pages on Cakemoe.
The Kiss x Sis manga is already finished and it has had some anime adaptations.
Kiss x Sis synopsis
After Keita Suminoe’s mother passed away, his father promptly remarried, introducing two step-sisters into Keita’s life: twins Ako and Riko. But since their fateful first encounter, a surge of incestuous love for their younger brother overcame the girls, beginning a lifelong feud for his heart.
Now at the end of his middle school career, Keita studies fervently to be able to attend Ako and Riko’s high school. While doing so however, he must resolve his conflicting feelings for his siblings and either reject or succumb to his sisters’ intimate advances. Fortunately—or perhaps unfortunately for Keita—his sisters aren’t the only women lusting after him, and there’s no telling when the allure of temptation will get the better of the boy as well.