Athrun

is a mysterious Demon who had saved Tatsumi Oga from Beelzebub when he was oversized. He appears in the manga only.

Appearence
Athrun has long black hair in a ponytail with bangs that hide part of his face. His attire consist of a robe that covers his whole body, clothing similar to the one the thieves wear, and he has a sword in his sash.

Personality
Athrun is shown to be a serious individual who is disappointed and annoyed with Oga's lack of familiarity with his abilities as a contractor. Athrun is also very cold, as he was ready to kill Beelzebub when Oga couldn't control him and only stopped because Oga managed to turned Beelzebub to normal.

Plot
He is a powerful demon who appears for the first time in Angelica's house in the demon world. At first, he appears to be working on commission of the thieves' leader as a body guard, but later he saves Oga and the others from being stomped flat by the giant baby Beel. When Athrun is disappointed that Oga when is unable to turn back Beel to his original size and decides to kill the rampaging Beelzebub, but Oga instinctively succeeds in doing so by telling Beelzebub that it's time for dinner causing Athrun to think they are too random. Athrun decides not to kill them and says that they should meet in the future before he teleports away. Athrun is later seen talking to his unknown boss and reporting on his mission, Athrun had infiltrated the thieves organization in order to recover thirteen stolen treasures, when Athrun tells his boss the he met the king's youngest son and his contractor he ask them if he should had taken care of them, but his boss tells that it's fine since he'll meet them in the human world and for now they should go along with the king farce.

Power
Athrun appears to be extremely powerful, as he was able to stop the giant baby Beel's foot with only one hand, and being capable of thr﻿owing him without much effort. He is able to teleport himself by using stones that Lamia describes as byproducts of dimensional transfer demons.