In Japan, a mysterious series of murders has occurred, which only targets people whose last name is 'Sato'. During a fight with a gangster, high school student Tsubasa Sato winds up in a parallel world. Things appear to be the same, but his friends and classmates are somehow different from who they used to be. Tsubasa doesn't understand what is happening around him. After seeing a girl killed in front of him by a pursuer, he finds out that he is now in a world where the lord of the land plays a lethal game of tag--a real onigokko (chasing game) that targets people whose last name is 'Sato'. If, during the 'game', a target manages to elude his pursuers for a few hours every day for a week, any wish that he has will be granted. Tsubasa discovers that the parallel world is linked to ours; when a person is killed in the parallel world, so is the target's counterpart in our world. When the siren sounds to signify that onigokko has begun, Tsubasa races to protect his sister's double--and hence his sister herself.