Leviathan

Maybe it's because of agoraphobia or if he lonely by nature, but he generally likes going inside of the coffin he carries around and spending time by himself. He envies even himself from a second ago, and deals with everything as fast and precisely as he can. He is a beloved king, and there is a saying that you shouldn't challenge Leviathan unless you are determined to kill every last population of Hades.

He brings unidentifiable creatures from the coffin he made to enter one day. Most of them are terrible beings and cosmic terrors that existed in the past, and meeting them means that you are at the end of your life.

“I'm sorry, but I'm currently busy."

"Dangerous elements? I will eliminate them." (Attack quote)

MC

Leviathan's first impression of MC was 'How come you're here again...?'.

Beelzebub

Leviathan thinks the king he's closest to 'doesn't exist', but Beelzebub believes he's closest to Leviathan.

Foras

Foras is Leviathan's right-hand devi. Foras tends to contact Leviathan often with worry, in case Leviathan brings in another right-hand devil who is worse than himself. (Of course, that never happens.)

Hades Devils

All the devils in Hades respect Leviathan as a father and king. In fact, they are all prepared to die with him by hanging themselves the moment Leviathan dies.

• Leviathan's gloves were made by a certain devil who cut his own skin off with the desire and obsession to touch Leviathan even like this.

• Leviathan likes to occasionally make Foras close his eyes to read the tattoos under Foras' eyes.