In 1405 A.D. humanity faced a devastating attack by Poltergeists—shark-like creatures wielding fire-based techniques. The Samurais, long scorned by the society, were the only ones who fought against the attack. However, their power wasn't enough to even harm Poltergeists. Just as hope began to fade, the arrival of Overheavens—mythical, animal-like beings—turned the tide of the war. With their aid, it didn't take long for Samurais to reclaim their land. The tunnel-creating abilities of the Poltergeists made it impossible for the Samurais to completely eliminate them, resulting in an eternal threat by Poltergeists, which frightened everyone, including the Samurais. This way, the need for safety and stability rose, leading to the establishment of ‘The Seven Unions’ to properly defend different regions of the world. Years later, a brutal invasion happened in a popular city called Zeche, in which Merogeo had to sacrifice himself, leaving behind his son Apollo and daughter Isleor. In that same attack, Apollo put his life in danger to protect his little sister from a Poltergeist, leading to an unexpected awakening of an Overheaven. The Poltergeist saw the potential in Apollo's willpower and his unique Overheaven. Recognizing that Apollo was still young and could eventually pose a threat later, the Poltergeist took him and Isleor to their hidden refuge, where they witnessed terrifying things... Less than a year later, Apollo managed to return to the land, having totally changed as a person. Living in a small, run-down house they found, they must hide from the Unions’ Samurais, keeping their experiences and all they witnessed in Poltergeists’ refuge secret, as it could bring humanity to a chaos..