Set in a futuristic era, Deava, an organization, combats the ancient and malevolent 'Shadow Angels' bent on humanity's annihilation. Unbeknownst to many, Apollo, a seemingly ordinary human, harbors the soul of Apollonius, a fallen Angel. With his allies, Apollo engages in a pivotal battle against Touma, a formidable Shadow Angel, to safeguard Earth from impending doom.