I've been looking for this one since forever.

Plot: A wimpy boy is being harassed by three girls into various sexual acts, girls tie his penis on a string, but then his penis falls off. Various graphic details ensues (don't want to go into too much detail, since 18+ is only a guideline...), his childhood friend steals his penis and rapes his mom... who is actually a witch and was the one who made his penis fall off. After a loooooong night of bumping uglies, wimpy Japanese dude emerges from the sunset a buff black male, who his mother calls "father".

Comedic hentai that doesn't take itself seriously. I've always wanted to read it again.

Thanks ^_^

Sei So Tsui Dan Sha

Yupp, that's it. Thanks a lot.