S01E01 Lost
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...
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.
After being devastated in the third World War (known as The Third Division), Japan was divided in two. Several years after the end of the war, a crime organization called Vischio has taken control of the destroyed city of Toshima (formerly Tokyo, Japan's capital city), where they are holding a battle game known as Igura.