Oathkeeper

After the end, a demon looks back to simpler times. Before he was wrapped up in a profession of violence and death, he saved lives and united the disenfranchised. Before his world-changing assaults, he was just a boy who grew up in Konoha's slums. Before he lost his name to history, known only as the Ghost, he was Naruto. (Disregards a fair amount of canon, and the timeline.)