Raphael

"A seraphim and the only one who understands Michael."

"'Raphael acts calmly when interacting with others, but it is said that when he's holding a spear, he can be even scarier than a demon. He respects Lucifer and Michael.'"

Raphael is a high-ranking angel of the Celestial Realm first mentioned in Lesson 44-3. According to Belphegor, he often looked after Michael's needs, no matter how unreasonable, and was meticulous and methodical.

Story
Note: this section may include spoilers

Background
Raphael was described to be like a demon in disguise due to his sullen expression.

Back when the seven brothers were angels, he had an antagonistic relationship with them; he would scold Asmodeus for attending parties, and Lucifer and Mammon would often gang up on them.