why ı can`t exist in every worlds

Kael Ardent is a young man living a meaningless life, until a mysterious cashier changes everything with a single sentence. Drawn into a dungeon he never chose, Kael is forced into a world governed by a system that treats life and death like numbers. But when his existence reaches the edge of collapse, something unknown awakens inside him — a state beyond death itself. This is the story of a man who should not exist… and the final breath that refuses to disappear. (ı`m new in this job and if ı do bad just say it please?)