The League of the Dark Swordsman

Christopher Sharp was a man who was minding his own business, heading to the place he was supposed to meet up with his brother and friends at, until he sacrificed himself to save a child. Then, he was given another chance at life, reborn in the world of Runeterra, as the physical manifestation of the darkness in existence, though he preferred to be called the Dark Swordsman.

Kamen Rider Calibur, and this is the beginning of his story.