Archdemon Asmodeus

probably garbage when it comes to common sense.

Origin
Born from Archdemon Lucifer. Goes on to destroy non-Abyss planets, yada yada.

Asmodeus, the Jailed Guardian
At one point, Asmodeus is in the Anime Universe = weird magics and can now be controlled but due to how powerful Asmodeus is, he tweaked the magics into where only one can wield his power. This chosen one soon showed himself and combined with the Archdemon to create Neo Archdemon Asmodeus, which provided more power. This fusion resulted in there being a line of chosen ones who could control Asmodeus, unlike how he planned where only one could control him. As a last ditch effort to never be found by these future chosen ones, Asmodeus fled to the most desolate place in the Anime Universe–The last gateway connecting The Abyss to the Anime Universe. The chosen one saw what the Archdemon was planning, and using the last dregs of his willpower and life, he bound Asmodeus to being a guardian against any of the Abyss that dared to cross the threshold practically closing the gateway almost like a stitch.

Trivia

 * The chosen ones usually have spiky hair, think Yugi from Yu-Gi-Oh.
 * Asmodeus often takes the form of a grand serpent.
 * Asmodeus originally looked like Archdemon Lucifer but with Archangel Hashmal's head. Yeah it was not a pretty sight.