Shiro Masakatsu is a boy people can't stand touching. One day, while walking, a floating bra falls around on his face. Wanting to find the owner, he looks around and gets splashed with water, thinking some big boobed girl was naked somewhere and playing with water, he rushes to find her, but instead he finds a bra-less girl, with water coming from a katana finishing a fight with someone, so naturally, he ran away. Later he meets the same girl at school, and another katana-wielder picking a fight with her. these are cursed katanas called youtou. Youtou cannot be used if the condition of the curse is not met, like with the girl's katana the katana of perversion, the youtou ganari, the katana that can only be used when feeling perverted.....hehe how dirty right ^.^