Togainu no Chi: Bloody Curs

Akira, the series protagonist, is a participant in a fighting tournament called "Bl@ster," after a successful battle, he retires to his quarters. He's awakened from sleep when a group of police break into his room and pin the blame for a recent murder on him, a crime which carries a sentence of life imprisonment. With no way to defend himself against the charges, Akira waits in fear for his life. He's visited in jail by a woman named Emma who offers him the only alternative to a life spent in captivity - join a higher-stakes fighting competition, and defeat the man at the top. Faced with no other option, Akira gathers his things and leaves for the city of Toshima, where the Igra competition is held. He has nothing more than the clothes on his back and the dog tags that peg him as a participant, so when some thugs show up to harass him and take a hit of a drug giving them super powers, he has little recourse. He's only saved by a man dressed in black, who brutally murders his attackers with his sword. The man threatens Akira as well, only letting him leave with his life when Akira shows too much pride to beg for his life.

After surviving his first day in Toshima, Akira is surprised when Keisuke turns up; he has followed him into the city. Not letting this change his mission they both set out into the city and are met by Rin who takes them to the Castle, the intake place for Igra.

After entering Igra, Keisuke is attacked by a mysterious blue haired boy who steals all of his tags. Akira stepping in defeats the stranger and reacquires the tags. Later on after losing an item belonging to his sister, the stranger grabs Akira and demands it back.