Read Absolution Manga
In real-life police departments, officers who work in Special Victims Units must rotate out, or otherwise, they become affected by the horrible things they see in the course of their jobs. Absolution explores the idea that if police departments employed superhumans, what if they were rare enough that they were the only ones who could do their job, and stayed in that capacity for too long, becoming mentally and emotionally destabilized. A superhero named John Dusk begins executing criminals after having seen too many horrible sights, believing they do not deserve to live because of the magnitude of their crimes.