Eriko Takahashi stands as the central protagonist of the narrative. Academically capable with consistently strong grades, she displays notable physical clumsiness and lacks athletic coordination in most situations—except when evading perceived threats, particularly escaping individuals she considers perverts, where she exhibits surprising agility. A naturally nosy and busybody tendency drives her to actively seek out and involve herself in others' problems, motivated by genuine curiosity and concern, though this can manifest as fickleness. She harbors a specific fear of injections. Her demeanor remains predominantly happy-go-lucky and carefree, cementing her role as an informal leader within her close-knit friend group. She speaks her mind readily, sometimes without full consideration of consequences.

Her closest companions are Yuma Suzuki and Ayano Sato. Eriko's relationship with Yuma originated in middle school through mutual dislike and conflict, a feud persisting into high school until Yuma ended it, forging a lasting friendship. Ayano, Yuma's lifelong friend, naturally integrated into Eriko's circle. Eriko expresses admiration for Yuma's younger sister, Momoka Suzuki, considering her adorable, good, and cute, while openly envying Yuma for having such a sister. Interactions with Akari Kouda began accidentally when Eriko fell on her twice before formal introduction; during a later investigation at a love hotel, Eriko clung to Akari. Eriko also observed peers like Yuma and Ayano during physical examinations, reacting with shyness when Ayano's outfit flipped.

Navigating high school involves distinct faculty dynamics. Eriko frequently encounters science teacher Yuichiro Odagiri, perceived as vain and perverted. While she often becomes the accidental or deliberate target of his actions, she occasionally turns the tables to blackmail him. Her experiences extend to interactions with other staff, including the infallible PE teacher Kaoru "Macho" Matsuo, who takes a particular liking to her, and the bitter health education teacher Kamei.