Modern World Warlock

Dante was an ageless warlock who had been going from one battle to another for hundreds of years. Following a chaotic encounter with an evil god, Dante unintentionally activates a contract with a demon, thrusting him into the modern world. Resolved to live a peaceful life, his intentions are halted when he finds himself in the middle of a conflict among rival mafia factions—dabbling with the ominous demonic magic that he knows best. — Description from novelcodex.org