Shaitan

"Anything darkness touches is mine. So if the light abandons you, I'll be there to pick up the rest."

- Shaitan Shaitan (シェータン(怨魂), Shētan (Enkon); Arabic for "Devil/Satan") is the current ruler of Gehenna, as such, she is addressed by her subordinates and citizens as Mephistopheles (メフィストフェレス, Mefisutoferesu lit. Not-Light-Loving). She inherited the throne after her father's passing, making her the second ruler of Gehenna. To humanity, she would be more known as the mythical "Demon King" (魔王, Maō), the ultimate ruler of Demon kind, though the descriptions of her address her as male, due to her father being the original Demon King.

As the ruler of Gehenna, Shaitan is also the only one who is of a higher authority than the Beasts of Gehenna, being loyal and chosen by her, and is also believed to be more powerful than the Beasts of Gehenna, arguably making her the overall most powerful known Demon of Gehenna.

Trivia

 * In Islam, the Devil is known as either "Iblis" or "Shaitan".