The year is 1943, during World War II. A desperate head of state in a European nation facing imminent defeat resorts to a ritual of summoning a demon, sacrificing not only enemies but also their own people. Against all odds, the ritual succeeds, and the summoned demon uses its power to defeat the enemy forces. However, instead of returning after fulfilling the contract, the demon summons other demons using the slain soldiers as sacrifices. These new demons, unbound by the initial contract, kill everyone involved in the summoning, including the head of state, thus freeing themselves. This marks the beginning of a war between humanity and demons. Roughly 100 years later, humanity continues its struggle against these demonic forces.