Hatoko "Petoko" Fujimura is a member of the PetoPeto yōkai race, distinguished by her ability to adhere to any person or object she adores through skin contact. This bond releases only when she falls asleep, a trait causing her deep embarrassment as it reflects her species' traditional method of attracting mates. Her physical existence relies on consuming love as sustenance; without sufficient emotional nourishment or nutrition, she gradually becomes transparent and risks molecular-level disappearance—a vulnerability she can partially control but not entirely prevent. This fuels profound anxiety about extinction, intensified by her mother's loss of three daughters who faded shortly after birth. Consequently, her mother pressures her to bear children for species continuity.

Petoko displays an innocent, caring, and occasionally naive personality, actively engaging in others' lives to cultivate happiness and friendships. Her movements produce a distinctive squeaky sound. She develops romantic feelings for her human classmate Shingo Oohashi, whose emotional support provides essential love for her survival. Their relationship explores human-supernatural coexistence, with Shingo's acceptance alleviating her fading fears.

Her family includes father Fujimura Tonio and mother Fujimura Maruko, who often appears partially transparent. Petoko attends school alongside diverse yōkai peers like kappa sisters and a nurikabe, navigating everyday social dynamics while confronting prejudices against "specified races." Her character arc emphasizes emotional dependence on Shingo and the tension between species-preservation expectations and personal desires.