Yagi Takeru, orphaned young, was raised by Tōma Rokunosuke, head of the Tōma household. He lives with the family and attends Izumo Academy as a high school student. His days blend academics with intense kendo club training, fostering a fiercely competitive yet close friendship with his best friend and primary rival, Yamato Takeshi. Deep bonds with childhood friend Osu Seri and the Shiratori sisters, Kotono and Asuka, anchor his stable life until catastrophe strikes. A powerful earthquake shatters Izumo Academy, transforming it into ancient ruins. Teachers and students vanish instantly.

Regaining consciousness amidst devastation, Takeru finds Seri and Asuka. Together they flee, only to discover their entire town deserted. Mysterious cloaked figures appear, revealing they have been transported to an alternate world. Here, Takeru is given a critical mission: forge a relationship with this world's princess to produce a warrior heir destined to change the world's fate.

Thrust into this unfamiliar realm, Takeru must adapt and survive. His honed kendo skills and martial prowess become vital tools against new challenges. Interactions with the cloaked figures and other inhabitants drive his actions and growing responsibilities. As he navigates this displaced existence, his connections to Seri, Asuka, and Takeshi remain powerful influences on his decisions and emotions, while the weight of his imposed duty adds complex layers to his role within the group and their unfolding narrative.