YuYu Hakusho

Teenage delinquent Yusuke Urameshi dies saving a child's life and is given a second chance as a Spirit Detective, investigating demons and supernatural threats slipping into the human world. He's soon joined by Kazuma Kuwabara and two former demon outlaws, Kurama and Hiei, in a series that moves from street-level cases into an escalating tournament arc among the demon world's strongest fighters.