I'm the Human Who Hunts Fiends

Theo awakens as a condemned prisoner in a deadly arena, where the Last-Stand Protocol lets him trade years of his life to reflect fatal attacks back at his enemies. After killing a tiger fiend and gaining its powers, he sets out to find his missing sister, battling monsters, corrupt cultivators, and a trafficking ring along the way. But every victory costs him years. With only two years left to live, Theo enters the Metropolis of Fiends, where his mysterious bloodline has made him prey.