Only My Psycho

This is District A, a jumble of skyscrapers and slums, somewhere in Asia. Sakaki Takeru, who grew up in such a place, is scouted by an underworld organization's assassin squad and, under the guise of recruit training, becomes partners with Atonashi Isagi. Upon their first meeting, Takeru falls for Isagi's looks, gentle personality, and the fact that he's still a virgin. As a perfect match both professionally and physically, they seem to be off to a smooth start. Until "something" happens that provoked Isagi's wrath...

(Source: Taiyo Tosho, translated)