In 2654, monstrous creatures emerged from the Earth, nearly wiping out humanity. Four legendary heroes fought back, saving the world—but at a great cost. Now, in 3128, the world is rebuilding, but all is not as peaceful as it seems.

Oka Katsuro, descendant of the hero Taira katsuro, thought the horrors of the past were over. That is, until he meets Asagi, a mysterious girl fleeing a parasite-like monster from underground. As Oka uncovers a terrifying secret, he must confront the dark truths his mother warned him about—and prepare for a battle that could once again threaten the future of humanity.