In a certain era, on a certain continent, there lived humans and creatures that could not be called humans.
The seven sealed demon kings released their souls to find creatures suitable for their sins in order to be able to move around.
The host can use the power of the demon king, but the price is to let the demon king's soul reside in his body. But if the host is too weak, it will be swallowed by the power, and the demon king will also lose his host.
The story begins with the story of the seven demon lords' lodgers.