 300 years ago, legendary swordsman Yagyu Jubei led his clan of samurai triumphantly against the villainous Ryujoji clan. On his deathbed, Yagyu transfers his abilities into a heart-shaped eyepatch which he instructs his attendant, Koinosuke, to bestow upon a worthy successor. In the present day, Koinosuke (whose aging has been all but stopped) finds this successor in perky schoolgirl Nanohana Jiyu, who her father, coincidentally, has nicknamed "Jubei." Unfortunately for Koinosuke, Jiyu doesn t want to embody the spirit of Yagyu Jubei. The descendants of the Ryujoji still bear a grudge against the Yagyu, so Jiyu reluctantly accepts the eyepatch to become Yagyu Jubei and put an end to the centuries-old feud.