Devil 17 - Hokago no Kusenshi

During a terrorist attack that results in the deaths of all his classmates, Tohru Kuroe witnesses another woman perish, prompting him to grab a discarded gun. A violent transformation occurs, and when he regains consciousness, he realizes he has become a killer. Tohru later discovers he was genetically modified for this purpose and is assigned the codename D-17. As he attempts to maintain a normal life, he faces threats from individuals targeting him and those close to him.