An encounter with a trio of bandits unexpectedly reunites skilled sorceress Lina Inverse with Naga, a fellow magic user who considers herself Lina's rival. Taking advantage of a plundered discount coupon, the food-loving duo make their way to Mipross, an island famed for its hot springs but shrouded in mystery.

While Lina enjoys her stay, she desperately tries to ignore the strange dreams that have been plaguing her for some time, especially since setting foot on the island. With her relaxation under threat, Lina is dragged into a request from the king alongside Naga, leading to an incident that will change the fate of the Island of Promise forever.