In his past life, he was the Great Demon King, but now he is a wielder of sealing magic. Since reincarnating as a human, he has a younger sister named Rinne. He overwhelms opponents with the transcendent physical abilities he retained from his past life, and since gaining magic, he applies sealing magic in various ways. He uses techniques like God's Chains and Magic Expansion: Sealing Domain. He is obsessed with magic. He acts blunt but kind toward his acquaintances and Rinne. He is male and speaks casually to everyone.

In her past life, she was Samsara, an aide to the Great Demon King. She is now human. While not quite on Mitsu's level, her physical abilities are relatively high. As a human, she wields magic with extraordinary talent, capable of using various spells at a high level. Furthermore, she can perform Double Casting, which is considered extremely difficult. She is very clingy and doting toward her brother, Mitsu. She has yandere tendencies and tends to go a bit wild when Mitsu is involved. She is female and speaks politely to everyone.

One of the Ten Kings who rank at the top of the academy. Like Rinne, her magical talent is exceptional. She primarily uses time-manipulation magic. While her talent is great, she reached the rank of Ten King through sheer effort. For some reason, she loathes the Great Demon King and demons, though the reason is... She is female and is in a fake relationship with Mitsu. She occasionally shows a tsundere side. She generally speaks politely to everyone.

A half-human, half-demon hybrid who wields body-strengthening magic. Her fighting style combines demonic physical strength with human body-reinforcement magic. She was raised by Phantom, and though they aren't blood-related, they share a bond like a real mother and daughter. She is the only person at the academy who knows Mitsu's past life was the Great Demon King. She is female, slightly possessive of Mitsu, and acts like a bratty kid.

Formerly an aide to the Great Demon King with deep loyalty to him. Although Phantom hates humans, her loyalty remained unchanged even after the Great Demon King (Mitsu) became human. She is a top-tier figure among demons, to the point where the Great Demon King once said, "There are only about ten people in this world who could beat Phantom." She overwhelms others with her physical prowess, but nowadays she creates various magic tools and can use all of them perfectly. She has lent several to Shizuku. She is one of the few who knows Mitsu's true identity and acts as a mother figure to Shizuku. Though Shizuku was originally created in an experiment, Phantom grew to love her while raising her, and they are now like a real family. She is female and generally polite to everyone, but speaks casually to Shizuku and uses extra-formal language with Mitsu.