All for One

All For One (, Ōru Fore Wan; lit. "Unmatched Greed of the Avaricious Demon Lord") is an incredibly dangerous form of the Black Arts, created some millennia ago; it serves as the embodiment of loneliness, solitude, and "strength through one's efforts without aid".

Due to its mechanics, its used by various Dark Mages throughout history — serving as their desire to become stronger in order to dominate all others and showing little trust in those around them; it also has the potential to create an "Ultimate Mage" (最高魔道士, Saiko Madōshi), something speculated by many of its users — though this is merely theoretical.

It's currently labeled as a Forbidden Magic by various government officials and the upper echelon of the Magic Council due to the gruesome side-effects it has on the victims. Created by an unknown evil Mage, it serves as the natural antipode of One-Banner Unison — so much so, that the two cancel each other out when used in each other's presence. In the modern era, there are only five known users — all of whom are masterful with the Black Art in their own right.

Trivia

 * This is, more or less, based on the same power from the anime/manga series, Boku no Hero Academia.
 * To be fair, since the aforementioned is a form of energy absorption, it's safe to say that this technique is based any and all power absorption techniques used throughout anime in general.


 * The reason that it serves as an antipode to One-Banner Unison is because of the symbolism in both techniques. The former represents "strength through loneliness, becoming an overwhelming power without reliance" and the latter represents "strength through unity, accumulating power from one's bonds".