Purgatory (Rengoku)

A manga/webcomic set in modern times, this story centers around Slip E. Lexington, a loner ex-assassin trying to live a life of peace. He was killed by his friend sent by his former boss for leaving the job, then resurrected by a deity like being, now hes on a path for vengeance against those who've wronged him so that he can be at peace. But in order to obtain peace, he has to go through war.