Heart Work Symphony of Destruction

Yuu Asakura was a mild mannered university student until he found a mysterious duffel bag with a gun and orders for an assassination. He was terrified at first, but when he held the smooth metal of the pistol in his hand, he started to become someone else. Capable of anything, Yuu takes the assassination job and enters a world of nonstop sex, blood and guns. (vndb.org)