Yui Hayakawa, 16 years old. She is a high school girl whose only strength is her running skills. One night, his younger brother, Takeru, builds a machine that sends her back in time to the Warring States period. Yui desperately joins the foot soldiers and passes herself off as "Yuinosuke". A handsome young warrior appears before her, and she falls in love with him at first sight. He is the legitimate heir of the Hagi family, Kuhachiro Tadakiyo. As it happens, Yui finds herself staying with Yoshino, a farmer. She goes to the castle with the sole intention of seeing Tadakiyo again.