All over Japan, people with the last name 'Satou' start to die in mysterious ways. Satou Tsubasa is a young man with a mentally disabled sister, who one day teleports to a parallel world by accident. There, the people he knows seem to be slightly different. His sister is healthy, and his enemy becomes his best friend. Together they fight for survival during the 'real onigokko', a game responsible for the Satous dying in the real world.