A first-year high school student at Kamome Academy, Nene is an earnest, romantic girl who dreams of a dramatic love story. She's insecure about her thick legs (which she calls "daikon legs") but is otherwise cheerful and kind-hearted. After a failed love confession, she seeks out Hanako-san, the famous toilet ghost, hoping to make her love life work out. Instead, she ends up becoming Hanako's assistant and bound to him as a pact. Nene gets cursed early on — she's turned into a fish-like creature after eating a mermaid's scale, which gives her a connection to water and a limited lifespan. She's brave in her own way, often putting herself in danger to help her friends, and she develops genuine feelings for Hanako. Her naivety sometimes gets her into trouble, but her empathy is her real strength, allowing her to see the humanity in even the most dangerous supernatural beings.

The main supernatural of the series, Hanako is the Seventh Wonder of Kamome Academy: "Hanako-san of the Toilet." He appears as a pale, small-statured boy in an old-school uniform, always wearing a white seifuku hat. Despite his childish appearance and mischievous personality, he's one of the most powerful beings in the school, wielding a knife and commanding the boundaries between the human world and the "Far Shore." Hanako is actually Amane Yugi, a human boy who died tragically in the 1960s. He became a supernatural bound to the school, tasked with maintaining balance between worlds. He's playful, teasing, and often flirts with Nene, but underneath lies deep sadness, guilt, and loneliness. He carries the burden of his past — including killing his own brother, Tsukasa. His wish is to protect Nene and undo the fate of her shortened lifespan, even if it costs him everything.

A first-year middle schooler and a member of the Minamoto family, a famous line of exorcists. Kou is energetic, righteous, and deeply wants to be a strong protector like his older brother Teru. He wields the sacred Raiteijou staff and can summon lightning, making him a formidable exorcist even at a young age. Despite his family's mission to exorcise all supernaturals, Kou is compassionate and questions whether all spirits deserve to be destroyed. He becomes an ally of Hanako and Nene, often torn between his duty as an exorcist and his growing friendships with the supernaturals. He's particularly close to Mitsuba, a ghost he tries to save, and struggles with his feelings of inadequacy compared to his brother. Kou is loyal, earnest, and matures significantly through the series, learning that strength isn't just about power — it's about protecting what matters.

Kou's older brother and the strongest exorcist in the Minamoto family. Teru is a high school student who's charismatic, handsome, and terrifyingly powerful. He wields a massive sacred sword and can exorcise supernaturals with ease. He's charming on the surface but ruthless underneath — he believes all supernaturals should be eliminated without exception. Teru is a major antagonist in some arcs, directly opposing Hanako and his group. He genuinely loves his younger siblings but his methods are extreme. His confidence borders on arrogance, and his worldview is challenged as the series progresses, especially through Kou's influence. He represents the "lawful" side of the supernatural world — bound by duty, not compassion.

The supernatural of the 4pm bookstacks. Tsuchigomori appears as a tall, glasses-wearing man in a lab coat — actually a teacher at the school. He's the 5th wonder and always bickers with Yako. 2nd wonder but cares for her. He's one of the more neutral supernaturals, often helping Hanako and the others while maintaining his own agenda. He was once a human teacher who cared deeply for Amane (Hanako) and knows much about the past. He's wise, pragmatic, and serves as a source of information about the school's history and the supernatural rules. Fifth wonder.

The supernatural of the "The Misaki stairs" rumor. Yako takes the form of a fox spirit, often appearing as a woman in a kimono or a small fox. She guards the boundary of the stairs and has a mischievous, trickster personality. Yako is obsessed with Misaki, a teacher who cared for her when she was a young fox statue near a old shrine but something happened to Misaki and she is desperate to have him back. Has a fox and human form.

Nene's best friend — a beautiful, kind, and popular girl who seems to have a perfect life. She is secretly in love with her childhood friend Akane-kun (the clock keeper and Fourth Wonder), though she constantly denies it. Aoi's cheerful exterior hides deep insecurities and a sense of being trapped by her family's expectations. She becomes a key figure in the series when she is chosen as a sacrifice for the school's mysterious "boundary" ritual, revealing that her fate is intertwined with the supernaturals in ways she never understood. Her arc explores themes of fate, sacrifice, and the courage to choose one's own path.

The First Wonder, the Clock Keepers, who controls time at school. Stoic and duty-bound, he can stop or rewind time with his pocket watch. He loves Aoi Akane, but his role as a Mystery conflicts with his feelings.