God of Killers

Gungnir, the most feared killer in the criminal underworld, decides to retire from his profession to keep a promise he made to the love of his life. But on the night of his final job, his partner betrays him, and he and his lover are shot. He survives by an apparent miracle, only to wake up in the body of a high school student. Determined to uncover the truth behind the betrayal, he vows that in this second life he will seize the happiness he was denied.

(Source: WEBTOON)