"Period" is how magic users called who beat "Spiral"—monsters that were summoned from isolation. Due to the rise of these beings, 14-year-old apprentice Period Haru, who is a part of the Eighth Arc-end Division, is called to break the cycle and cast himself into the endless battle. However, a mysterious thievery occurred and sank the division into bankruptcy, forcing Haru and his other comrades have to leave their headquarters. To rebuild a branch, they have to overcome quest after quest.