Evil God of the Abyss

Evil God of the Abyss (深淵の邪神) is an Outer God, whose real name is unknown.

Background
At one point, Katsushika Hokusai encountered the Evil God of the Abyss, which caused him to later become a Foreigner Class Servants.

Creation and Conception
The Evil God of the Abyss is likely adapted from of the Lovecraftian Mythos.