Koitsu-ra no Shoutai ga Onnada to Oredake ga Shitte Iru

Synopsis:

Makoto and Shinobu were childhood buddies who regarded each other as men among men. Ryunosuke shared a room with them in the school dormitory and had the impression that he was about to begin on a rough yet manly adolescence. However, her true identity was a woman! And the two of them! As a result, Ryunosuke's childhood grew extremely obese, wicked, and sloppy!