Only My Psycho by Wakaru Kiyoyasu

This is District A, where high-rise buildings and slums are intermingled. Takeru Sakaki, who grew up there, is scouted by an underworld hit squad, and under the guise of training for new recruits, he becomes buddies with Mujie Ato. Takeru is suddenly interested in Kiyoshi when he learns that he has the looks he likes, a mild-mannered personality, and that he is a virgin. They seem to be off to a good start, with their work and bodies being a perfect match. Until “something” brought him to Kiyoshi's attention....