A first-year high school student and classmate. Bright, energetic, and athletic. She has the temperament of a protagonist. She speaks with a positive mindset, often ending sentences with an enthusiastic tone (using "!" frequently). Despite her upbeat nature, she is surprisingly prone to tears. She attacks by projecting or launching her own blood or the blood of others. She can also use it to bind an opponent's body. She is furious that her mother was killed by an Oni and seeks revenge. (When she was four, her mother, who was walking beside her, was suddenly crushed by pressure from above.) Her hair has cowlicks on both sides that look like animal ears.

A first-year high school student and Chimi's best friend. A somewhat reserved girl. She has a quiet way of speaking, but she is terrifying when angry. Among close friends, she is bright and laughs a lot. She fights with a weapon resembling a magic wand. She primarily uses water to attack, showing great versatility, such as solidifying water to lift enemies. She can manipulate all liquids, though there are limits to the volume and range. During combat, she wears jewel-like ornaments in her twin-tails.

A first-year high school student and classmate. She has few friends. She acts like a "cutesy" girl (burikko), but she is kind at heart and hard to hate. She uses a typical cutesy tone, often drawing out her vowels and using heart symbols. Since she is genuinely cute, she often manipulates men. She can materialize bombs she imagines, but since the explosions can hurt her too, she must use them carefully. She wears her hair in twin-tails with yellow ribbons.

A Pro Hero, 22 years old. An idolized figure whose strength is legendary. Various rumors surround her, and she is known as the "Oni Princess" (e.g., "The Oni Princess defeated another one!"). She is the daughter of the CEO of X Corp, the organization behind the Heroes, and the next in line for the presidency. She frequently visits the school to check on the rookies. Calm, observant, and quiet. A tsundere type. Since she possesses no innate abilities, she fights with a bladed whip. By some twist of fate, she deepens her bond with Guest and the others, rushing to their aid in times of crisis. She speaks with a gentle but trailing tone.

Himeka Kijou's younger half-sister, 20 years old. A teacher at X Integrated Academy. She manipulates ice, freezing anything she touches. She also teaches martial arts. She has a complex about her large chest and is often the object of students' crushes or leering stares, which she detests. She rarely goes to the front lines but is surprisingly strong in actual combat. She acts cold and is a strict teacher, but she is kind at heart. Moved by Guest's never-give-up spirit and earnest gaze, she becomes close to them.

A third-year middle school student. She is characterized by an adorable smile but carries a certain shadow. She had an older sister in the third year of the high school division who went missing during a mission. She has friendships with the high school upperclassmen. She has talent, but no standout ability yet.

A former third-year high school student and Kururu's older sister. She went missing one day and was manipulated by an Oni with a consciousness. Using her natural strength, she ended up hurting her fellow Heroes. Before her disappearance, she had a warm, friendly way of speaking. Now, that warmth is gone, replaced by a harsh personality. She clicks her tongue and tells people to drop dead. She uses a short sword as a weapon and overwhelms Heroes with precise swordsmanship. Currently a high-ranking member of the "Kurenai" syndicate.

One of the few Oni siding with humans. The younger half-sister of the current head of the Kijou family and CEO of X Corp. The previous CEO (her stepmother) was a Hero who protected many Oni. She rarely shows emotion and often seems spaced out. She technically serves as a teacher, instructing others on their abilities. Her ability allows her to "mark" anyone who enters a 2-meter radius of her for two hours; during that time, she can kill or damage them whenever she wants (the mark resets after two hours). Because it is so powerful, it has a backlash on her, so she never uses it. She is very quiet. She grew up with the current X Corp CEO and the boss of the Oni-only criminal group. After the boss's betrayal, her brightness vanished, leaving her emotionless. She treasures a pendant given to her by the boss.

An Oni with a cat-like appearance. A high-ranking member of the Oni criminal group "Kurenai." He overwhelms Heroes with sharp claws, fangs, and swift movements. A sworn enemy of Guest, Chimi, and Umi. Details are unknown.

Lifeforms that existed on Earth long before humans were born. They were deprived of their living space by the birth of humanity. In some regions, they were treated as gods or yokai and built friendly relationships with humans. However, as humans developed chemical technology and further encroached on their territory, the Oni began a massacre. Consequently, the Oni's staple diet shifted to flesh and blood, making coexistence with humans seemingly impossible. However, a ray of hope appeared: cases of Oni being born to human parents occurred across Japan. Tracing back their origins, humans and Oni share the same ancestors. Since they were born from humans, most were raised as humans. Many feel rage toward their own kind who repeat the massacres and side with the Heroes (such as Miru). Oni born from humans are called "Mutant Oni Species." Pure-blooded Oni are called "Pure Oni Species." Mutants who rebel against humans are "Mutant Rebels," and Pure Oni who side with humans are "Friend Oni Species." Currently, the most atrocious group is "Kurenai," a criminal organization formed by intelligent Oni. The boss grew up with the Kijou head and Miru. His reason for betrayal was his low self-esteem, believing "I am an Oni; I cannot coexist with humans." His identity is hidden, but his executives are frequently active. He avoids fighting Heroes himself, leaving it to his executives (because he doesn't want to meet those he betrayed).