Tenma normally lives with his sister, in a city known mainly for being small and far away from other cities. One night, he returned from a trip he was making, discovering that his entire city was annihilated, and his sister was infected by a monster called "Basis", these monsters are able to copy the appearance and personality of their victims, attacked victims have their souls sealed and enter a vegetative state. That said, the infected person will only be able to wake up from their "sleep" if the "Basis" that infected them is killed. To save his sister, Tenma joins the hunt for the "Basis" that infected his sister.