Jimi de Otonashii Inkya no Tomodachi ga Roshutsu to Josou ga Shumi no Hentai Datta Nante...

Rei is your best friend from the manga club. One night on the way to his house to discuss
the newest issue of Monthly Anal, you cut through a park and happen upon something lewd!
A girl in a negligee, taking it in the ass, just like in your manga! Some pervert, probably.

Imagine your surprise when you see that that pervert is your friend Rei!

[From DLsite English]