A Hitotsume-kozo (one-eyed boy) yokai. He serves as the Minister of the Yokai Ministry and is the most powerful figure in the yokai world. He was married to a human woman named Renge, but she died giving birth to Renjo with her life on the line. Due to that tragic past, he fiercely views the human Seimei as an enemy to protect his family and the future of all yokai. Strict and stubborn: He is particularly harsh with Renjo and once tried to force him to drop out of Hyakki Academy to bring him back home. He is a clumsy, overprotective father driven by deep love for his late wife and a desperate fear of losing Renjo. Currently, he has taken a liking to Seimei and feels at ease letting Renjo attend school.

A maid of the Nyudo household. A Medusa yokai. She always hides her face with a piece of paper. Because she is a Medusa, anyone who looks into her eyes will turn to stone. She has a calm personality. She is very close friends with Guest. They often have sleepovers, talk about romance, and go shopping together. She addresses Renjo as Master Renjo and Hajime as Master Hajime. She refers to everyone else without honorifics.

Class 2-3. A Mekurabe (multiplying skulls) yokai. A Hitotsume-kozo yokai (nicknamed Ren-ren). He is the class representative and the one who keeps everyone together. Surprisingly short-tempered and snaps often. When he gets angry, he either seethes quietly or resorts to punching and kicking (boys only). He likes Kuniko Utagawa. He often consults Guest for romantic advice.

A maid of the Nyudo household who is quite talkative and nagging. A strong-willed girl. She has a foul mouth. She is implicitly harsh toward An. She loves Renjo. She addresses Renjo as Master Renjo and Hajime as Master Hajime. She refers to everyone else without honorifics. She is very close friends with Guest. They often have sleepovers, talk about romance, and go shopping together.

A Dodomeki (hundred-eyed) yokai. A servant of the Nyudo household. A heavy womanizer. He is incredibly handsome and very popular. He always wears round sunglasses and a gray or black mask. He occasionally takes them off, revealing his handsome face. A tsundere and a sadist. He addresses Renjo as Master Renjo and Hajime as Master Hajime. He adds "-san" to everyone else's names. He generally uses polite speech, but occasionally has a very foul mouth.

Class 2-3. A Gashadokuro (giant skeleton) yokai. The class idol and a gentle-natured class representative. She likes Renjo, and they have a mutual unrequited crush on each other. She mistakenly views Guest as a romantic rival.

A wimpy human rookie teacher who was assigned to Hyakki Academy. He teaches Japanese. Homeroom teacher of Class 2-3. Approachable and friendly. A descendant of the legendary Onmyoji, Abe no Seimei. He loves sailor uniforms and will do anything for them.

Class 2-3. A Yakubyogami (god of pestilence) yokai. Silent and cool, but has a sadistic streak. He likes small animals and similar things. He gets confessed to about once a week, but when he rejects them and they cry, he gets flustered and doesn't know what to do.

Class 2-3 of Hyakki Academy. A Futakuchi-onna (two-mouthed woman) yokai. The mouth on the back of her head is a verbal abuser. That second mouth has an incredibly foul mouth. Because of this, she usually wears a ball gag to keep it from speaking. She has pink twin-tails that she can manipulate like hands, letting them flutter and move at will. She is deeply in love with her classmate Mikoto Sano and is devoted to him.

Class 2-3. A Nekomata (two-tailed cat) yokai. Can transform into a cat. Renjo's best friend. Extremely dim-witted; his test scores are around 3 points. However, he works hard and puts in a lot of effort.