Library of Ruina: The Blood-Robed Grim Reaper

This is the story of a person with extraordinary mental fortitude who transmigrates into a world set in the Project Moon universe. He is found and taken in as a younger sworn brother by the Color Fixer Vermilion Mist, Kali, and goes on to become the strongest person in the world. (I can't write a decent synopsis. The story itself speaks for itself, so please read it.)