Onitsuka Miaki, a freshman from Fujimigahara Girls' Academy Naginata club, is going to a training camp on a remote island that is owned by her captain, Igasaki Kotone, along with 11 members. Legends say that the remote island is a place where the worst bandits live who have hidden a national treasure beneath the island. Everything is still normal until one of their members gets killed. Their life-threatening experience begins then.