This is the story of a young Mexican who, by killing a god in a stroke of luck and skill, achieves the highest level of magic.
Summary
From myths and legends, they were born. The essence of the world and beyond, this is what comprises the supernatural core of them, thus lending form to these existences, the gods. But for some gods, the forms and nature of their myths becomes a burden, and they rebel against them, manifesting in the world, escaping from the myths and legends, also known as the Domain of Immortality, as Heretic Gods, and bringing disaster with them.
What determines the power of a Heretic God is not their fame, or how powerful they were portrayed in their myths, but rather their own will and determination.
There are also some cases in which Heretic Gods lose part of their divinities as a result of being wounded or sealed. Sometimes, these lost pieces have been put into Grimoire. In these cases, they are shown to experience change in their personalities. The example of this can be seen from how Verethragna, Sun Wukong, and Lancelot all showed changes in their personalities once they regained their full power and Athena who lost her memories and personality after part of her power was absorbed by Metis (Anime Only). Regaining the lost piece will return the Heretic God to their normal selves.
Powers and Abilities
Heretic Gods are endowed with divine powers and weaponry called Authorities which embody their right to rule in the myths. These Authorities can sometimes be quite different from the modern version of the god, reaching back to the origins and history of the myths and legends from which the Heretic God was born. For example, Athena's petrifying gaze, which she shares with her alternate identity of Medusa, or Apollo's power over wolves.
Heretic Gods are supernatural beings thus make them invisible to normal people. Only mages, witches, priests, Hime-Miko, and those with some touch of the supernatural can see them according to the anime, though the Light Novels appear to contradict this. However, it 'does' confirm that Heretic Gods can choose whether or not to be seen.
Heretic Gods also can perform magics with much greater ease than mortals, even without using their Authorities, as Athena showed when she made the people around her not notice her, and by the actions of Sun Wukong.
Heretic Gods are immortal, living forever unless killed. Even if killed, however, a Heretic God will merely return to the myths and legends which spawned them, and may return to the human world in time. As long as their myths and legends exist, so too will the Heretic God in some fashion, as the myths are part of the Heretic God themselves, and the Heretic God is just the manifestation or extension of these myths. Also, Heretic Gods are immune to all mortal weapons, be they swords, clubs, guns, poison, chemical, or biological. Only the most powerful of magical weapons or spells can harm, let alone kill them. Heretic Gods can even survive without a physical body. This happens when they have drained most of their power, or have been badly, but not mortally, injured.
Heretic Gods can even seemingly possess people, though it is unknown if the possessed must fit any requirements to be eligible for this.