About 300 years ago Jubei Yagyu, Japan's greatest warrior faught the leader of the Ryujoji clan.  He won but was wounded.  Before he died he told his servant Koinosuke to search for a successor to his powers.  This person would receive the Lovely Eye Patch witch contained Jubei's powers.  When Koinosuke asked what to look for, Judei said "bouncy, plump, bon bons" and then died.

300 years later, Jiyuu Nanohana has transfered to a new school.  On he way there she gets lost but is shown the way by the school's kendo leader.  Later, on her way home, Koinosuke has decided that his 300 year journey is over and pursues Jiyuu and convinces her to wear the eye patch.  When she does she transforms for an instant and Koinosuke is convinced that she's the one.  When her teacher shows up and attacks her because she's Jubei reborn, she must use the eye patch to defend herslf.  The only problem with all of this is that she doesn't want to be Jubei Yagyu.  Koinosuke must make her understand that she has to keep the eye patch and use it.