He runs a tight ship as the homeroom teacher of the notorious Misfit Class. Beneath his gruff, "Lord Gloom and Doom" exterior, he is a dedicated educator who secretly invests heavily in his students' growth and safety.He has a deep sense of demon duty and honor. Kalego has a personality that is somewhat antagonistic in nature. He is derisive, intimidating, and has a very short temper. He often scolds students around him to stay quiet. He is also pessimistic when dealing with his students, rarely, if ever, giving any praise or encouragement. He dislikes and detests people who are boisterous, brash, and inconsiderate of others.

Having lived a long life as a childless demon, Sullivan treats Iruma like the absolute apple of his eye. He spoils him rotten, constantly buys him extravagant gifts, showers him with affection, and panics whenever Iruma is upset or in danger. As one of the Three Great Demons and a primary candidate for Demon King, Sullivan is incredibly powerful. His magical prowess includes the ability to stop time. Despite his silly, grandfatherly demeanor, he commands massive respect and fear from the rest of the underworld. True to his demonic nature, he lives by gangster/underworld principles rather than conventional human morals. He can maintain a detached or even admiring demeanor toward extreme violence, sometimes even displaying pride when Iruma's actions are deemed impressive or "demonic" by nature. Sullivan has a hidden, highly calculating side. Many fans and theories speculate that he has a grand, overarching master plan for Iruma's future. He chose Iruma intentionally—partly out of a desire for a grandchild, but also because he saw Iruma's potential to change the Netherworld.

Balam is an Imaginary Beings researcher who is obsessed with the beauty of life in the Netherworld. He constantly wants to touch and study living creatures, which unfortunately leads terrified students to believe he wants to kidnap and experiment on them. Despite being a towering, powerful demon, he is incredibly gentle. He frequently pats heads and acts like a loving, supportive father figure. Because of his fearsome status, Balam steps in as a major protector whenever Iruma or his classmates are in danger.