Muchi na Boku to Warui Koto.

A mopey gangster who's as loyal as he is violent and a top-dog delinquent who's a glutton for pleasure! These testosterone-filled teenagers are up to no good, in more ways than one! Wimpy crybaby Taichi goes to a school full of delinquents, but for some reason, all the bad kids in school think he's their leader! There's a secret only Taichi doesn't know... the fact that he has an alter-ego who's a ruthless delinquent! And, little does Taichi know, he sometimes regresses to a child-like state. He doesn't even know what touching himself is, despite his body being in the throes of puberty... Mitsuru Gunji, leader of a rival school's gang, takes interest in Taichi and starts initiating him into the ways of pleasure. After melting in Mitsuru's arms after his first time (mentally speaking), Taichi starts begging for more!