Hayakawa Yui is a 16-year-old girl whose only strong point is her ability to run fast. When her reclusive but genius younger brother invents a time machine, she accidentally gets sent to the Warring States era and meets the young lord of the Hagi clan, Hagi Tadakiyo, and falls in love with him. Upon returning back to her modern time, she discovers from her high-school teacher that the Hagi clan are doomed
