Katerea Leviathan was a member of the Khaos Brigade's Old Satan Faction. She was a descendant of the original Leviathan.
She and the other descendants of the original Satans (except Vali Lucifer) believed that the current Devil system was mistaken and sought to change it by killing the current Satans and taking control of the Underworld.
During the meeting of the Three Factions, attempting to kill both Sirzechs Lucifer and Serafall Leviathan but fought against Azazel instead after the latter made fun of her. While both sides were initially equally matched (due to Katerea absorbing Ophis' snake), the battle is overturned by the sudden betrayal of Vali Lucifer.
Despite this, she was still defeated by Azazel who revealed his Artificial Sacred Gear. In a final act of desperation, she converted her arm into indestructible tentacles and activated a powerful self-destruction magic spell, to which Azazel responds by cutting off his hand, telling her "I'll give you a hand, at least".
He then stabbed Katerea with a light spear, effectively killing her.
Katerea had the appearance of woman wearing a dress that was extremely low-cut and had a high slit on it which exposed a large portion of her breasts. Katerea hated the current Satans, believing that they were defiling the name of Satan itself.