Athrun

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

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, but later he saves Oga and the others from being stomped flat by the giant baby Beel. He considers killing Oga when he seems unable to summon Beel to him and revert him to his original size, but Oga instinctively succeeds in doing so and Athrun changes his mind.
 * He is able to teleport himself by using stones that Lamia describes as byproducts of dimensional transfer demons, and is last seen reporting to mysterious parties on his encounter with Oga. He is then told by his superiors that he will meet Oga again in the human world.

Plot
Athrun says that he will meet Oga again in the human world.

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.