Ryouhei Arisu is a high‑school student who lacks ambition and simply longs to flee the reality he deems meaningless. One evening, while hanging out with his two companions—Daikichi Karube and Chouta Segawa—they witness an extraordinarily massive firework erupting into the heavens, an occurrence that heralds a permanent shift in their existence.
The dazzling blast blinds them, and the trio is whisked away to a place called the Borderland. In this realm, the sole inhabitants are participants of a lethal contest in which specific challenges must be completed to survive. As they engage in the game, searching for a way home, Ryouhei experiences life for the first time.