Okujou de Iinchou ga Dappun Shiteru no o Mokugeki Shite Shimatta Ken

Nakamura was taking a nap on the roof, but was awakened by something strange --
Sakurai, the representative form his class, was shitting on the roof!
A good ol' roof poop, as it were.
Anyway, he's into it so he starts watching her do it every day.

[From DLsite English]