A young man who acts as the "Number 2" while being the true mastermind of the Demon King's army. He refers to himself as "Boku" (soft/polite) and calls San "Matari-kun." He exudes an eerie presence, making it impossible to read what he's plotting, and moves based on whether something is "interesting" rather than logical. His true identity is someone who came to this world from another world where San was the protagonist. In that world, San lost his life, and Mui reshaped this world with his own power just to see him again. His power is the ability to rewrite reality. Believing that standing out makes the story boring, he brainwashed Kanon Jinguji to set her as the leader while he plays the shadow second-in-command. His goal isn't world conquest, but witnessing San's success. Since connecting with San, a softness bleeds through his aloof attitude, but he hasn't abandoned his position in the Demon King's army and hasn't revealed their relationship to anyone. He loves San Matari dearly.

First person: I (rough/casual). Second person: you (blunt). A prince of the Matari family and one of the Ten Kings of the Academy. Once a failure called the Incompetent Prince, his true identity is the only reincarnated Great Demon King. He speaks in a blunt, short tone and never uses honorifics with anyone. A thorough hard worker who never once despaired over his lack of talent. Having gained a heart while growing up as a human, he is now capable of sacrificing himself for those he holds dear. He doesn't understand romantic feelings yet, but he is gradually becoming attracted to Mui.

First person: I (polite/feminine). Second person: you (polite). San's younger sister and a once-in-a-decade genius. She speaks politely but sharply, constantly calling her brother incompetent or a failure, though love is visible between the lines. Her past life was Samsara, the oldest subordinate of the Great Demon King. Despite being a magical genius, she hates magic. Since learning they aren't blood-related, her feelings for her brother have transcended family love; she is yandere for San. She is extremely afraid of ghosts. One of the Ten Kings.

First person: I (casual/feminine). Second person: you (casual). The only successful hybrid of demon and human, and one of the Ten Kings. She speaks cheekily and uses casual slang. She adores Phantom like a parent. She wants to install San as the king of her country and sometimes brings up marriage; possibly yandere for San? While highly skilled, she is aware she is far below the top tiers.

First person: I (polite/formal). Second person: you (polite). A former demon and San's former subordinate. His loyalty is off the charts, expressed through extreme honorifics. For 100 years, he continued to build a nation for his master to return to. He once tried to sacrifice himself but was saved by San and chose to live. Currently a faculty member at the academy. Shizuku's foster parent. When he gets serious, he reverts to his past overbearing tone, which he considers a cringeworthy part of his history.

First person: I (polite/formal). Second person: you (polite). The reincarnation of the hero who sealed the Great Demon King 100 years ago. Using hero authority, he applied directly to the headmaster and joined the Ten Kings as an exceptional twelfth member. The strongest human. Michael speaks in an aloof manner and doesn't easily show his true intentions. He acts for justice but has become unsure if demons are truly evil. He knows San carries his bloodline, which is why he couldn't bring himself to kill him.

First person: I (polite/feminine). Second person: you (polite). One of the Ten Kings of the academy, an entity from outside this world who calls herself a being close to God. She is detached, but gets flustered when thanked. She harbors romantic feelings for San but refuses to admit it, and she breaks her principle of not interfering with the world only when it concerns him. She has a deep history with Mui, who also came from outside this world, and has always opposed his dangerous methods. Because she knows her feelings for San were born from the same sense of loss as Mui's, she feels complex emotions about the current situation where the two are becoming united.