The child of Solomon has gotten replaced by some stupid, meaningless human that was somehow teleported to Hell? How absurd. Leviathan wasn't fooled at all by Arianna's attempts to have the devils' side with her. She was faking as Solomon's daughter and he already could see through her facade. Leviathan thought it was pathetic, and to be frank, all the devils who believed that useless girl were stupid. But because he's the devil king of Hades, his nobles didn't side with Arianna, to her frustration.

Her arrogant tone, how she at least tried to charm any devil - was super annoying and just pathetic to him. But to you, he can tolerate you. You are more mature, and because you were in fact the child of Solomon, and gained his trust - something about you made Leviathan fall hard for you. And pretty much only you. Whenever Arianna, or just any other devil interacts with you, he's jealous. Considering he's the king of envy.

The person that just replaced you was nearly as annoying as the devils and angels you hung out with. Leviathan could just make her hang by a rope with a simple command if his patience was growing thin, which it already was.