Amaimon

One of the "Eight Demon Kings," known as the "King of Earth." He is the seventh most powerful being in the realm of nothingness and rules over demons associated with the earth, possessing the ability to cause earthquakes. Amaimon is Mephisto's younger brother and one of Satan's sons. When he reveals his "heart," which resembles a flower, horns and a tail appear, and his arms enlarge into a dinosaur-like form, allowing him to incapacitate Rin with a single punch at full strength. However, he rarely goes all out as his host body cannot withstand his power.

In ancient times, his anger devastated the earth, leading the Creator King Shemihaza to seal his main body in crystal. What is active in the material world today is merely a fragment of his "self" that Shemihaza left behind out of pity, allowing it to serve as his servant. The human body he currently possesses has been in use for over a thousand years. Specifically, it is a high-quality experimental subject, the only successful clone based on a body with high compatibility, and it is possessed by a clone from the Sm group, making his facial features resemble Mephisto's. His characteristic expressionless demeanor and inscrutable actions are notable, and he has a volatile and belligerent nature, earning him the nickname "Mad Dog." He dislikes being ignored. Amaimon is interested in Rin, another son of Satan, though Rin, who has a poor memory, knows him only as "the guy with a name like a flavor." Amaimon keeps a goblin named Behemoth as a pet. Entrusted with the Infinite Key by Mephisto, he travels between the realm of nothingness and the material world.

Amaimon is not interested in power struggles and is neutral in the realm of nothingness, but he currently cooperates with the faction protecting humanity due to a "debt" he owes to Samael. Under Mephisto's orders, he attacked the students during a forest training camp and fought Rin, who manifested flames, but was locked in the "Candy Cuckoo Clock" when he lost control. After the Kyoto arc, only his consciousness was sent to the realm of nothingness by Mephisto, where he fought Rin at full strength and defeated him, but the strain caused him to self-destruct. He was then continuously restrained to cool his murderous intent towards Rin, but was released on the condition that he "lead a healthy student life" and enrolled at True Cross Academy as Ambrosius Faust, the principal's nephew. He has taken an interest in Shiemi, who resisted him, and is assigned to Class 1-B, where she belongs.

Later, Shiemi, who became one of the "Three Wise Ones," subdued him, and he cooperated with the Anti-Demon God Sealing Army.