Before eradicating humankind from the world, the gods give them one last chance to prove themselves worthy of survival. Let the Ragnarok battles begin.
Rai wakes up from 820-years long sleep and starts his new life as a student in a high school founded by his loyal servant, Frankenstein. But his peaceful days with other human students are soon interrupted by mysterious attackers known as the "Unions".
Saya Kisaragi is an outwardly normal girl who serves as the shrine maiden to a country town; in reality, she is a skilled swordswoman charged by her father to defeat Elder Bairns, monsters who feed on human blood. As her battles grow more desperate and more people she cares for fall victim to the Elder Bairns, Saya begins finding faults in her reality, and eventually uncovers a disturbing truth about herself, the town and her surviving friends.
