Miko Yotsuya is a high school student burdened by a permanent ability: perceiving spirits, ghosts, and supernatural entities invisible to others. This spirit sight grants her total clarity for most apparitions, though the most powerful entities remain unseen, their presence revealed only through effects. The ability operates constantly, forcing her to witness horrifying and threatening entities during daily life, causing significant fear and distress. To avoid attracting unwanted attention or appearing disturbed, she maintains a stoic, unflinching facade despite intense internal panic, though this mask slips in moments of safety. Her sight does not extend to seeing human auras.

She resides with her protective mother, Toko Yotsuya, and younger brother, Kyousuke Yotsuya, neither aware of her ability. Her father, Mamoru Yotsuya, died before the series. Lingering regret stems from a past conflict with him over pudding, amplified by her occasional glimpses of his spirit. This family dynamic fuels her motivation to shield loved ones from supernatural dangers.

Her primary strategy is ignoring spirits to prevent interaction, but this proves difficult. Spirits obstruct her vision, nearly causing accidents like being hit by a truck, and their noises overwhelm human conversations. Coping mechanisms include wearing headphones and avoiding eye contact. Despite profound fear, she shows gradual development from passive avoidance to calculated intervention. Key actions include destroying a snowman spirit threatening Kyousuke, confronting the spirit haunting her teacher Zen Tohno (later revealed as his abusive mother's manifestation), and weakening the entity possessing Michiru Ichijou by acknowledging Michiru's true beauty. These acts demonstrate emerging bravery, often following intense reluctance.

Relationships drive many actions. She prioritizes protecting best friend Hana Yurikawa, whose strong spiritual aura attracts dangerous entities. Miko diverts Hana from spirit-infested routes, brings her food during spiritual sickness, and enters a risky contract at a mountain shrine to safeguard her. This contract, involving a "god" and two kimono-clad spirits, obligates them to save her three times in exchange for an unspecified price, later threatening Hana as the unwitting cosigner. She navigates complex ties with Yuria Niguredou (an initial rival medium), Mitsue Takeda (a helpful fortune teller), and Shindou Romm (a mysterious figure supplying temporary protections while amused by her struggles). Her relationship with Michiru evolves from terror (due to a tentacled spirit obscuring Michiru's face) to protective friendship after resolving the possession, with Michiru developing unreciprocated romantic feelings.

Notable traits include a deadpan snarker demeanor, especially with Hana; a love for pro wrestling inspired by "Anaconda the Badger"; and subtle visual tells of fear like gripping her skirt hem. Her surname "Yotsuya" references a famous Japanese ghost story and contains the kanji for "four," symbolizing ghostly connections, while "Miko" (shrine maiden) ironically contrasts her reluctance with traditional exorcist roles. Persistent challenges include traumatic encounters, like an axe-wielding subway ghost causing repeated soiling incidents, and consistently drawing bad luck fortunes at temples. Her resolve to live a normal life persists despite these supernatural ordeals.