As the general population becomes increasingly aware of the Aragami and the danger they represent, the Japanese government has come under pressure to take the one measure guaranteed to relegate the Aragami to the realm of legend once more. Now Momiji must be protected not only from the Aragami, but from the people who would sacrifice her save themselves as well. The TAC moves underground to continue the fight, as the country surrenders to the natural forces released by the rebirth of Susano-o. Time is running out and the final confrontation approaches in Blue Seed: Nightfall!