Yajiro is a mercenary hired to help save the life of a sensei held in a castle by a group of gun masters.  The gunmen overwhelm the ninja with their firepower and Yajiro escapes.  On the run, the comes across a girl in a hot spring who help hide him in a not so unpleasant way from his pursuers.  The girl is called Rushuna and she makes her way to the castle to try her form of battling - to win by taking away the opponent's will to fight - by smiling.  She discovers that this won't work for these guys though and so she displays some very impressive gun fighting skills as well as an unique method of reloading her weapon to save the sensei from the bad guys.