Iono Tomonaga, childhood friend to Hakone Oumi and her brother Sento, navigates a complex bond with the latter as unspoken romantic feelings clash with his ingrained view of her as a sister. Her quiet yearning fuels recurring frustration, amplified by Sento’s obliviousness to her emotions. A pivotal moment arises when her attempt to gift him a token of affection dissolves into distracted daydreams, causing her to overlook securing the student council room. This lapse enables the theft of both the school’s budget and her concealed present. Sento’s unintentional dismissal of her distress—reinforcing his sibling-like perception—precipitates a spiraling melancholy, drawing the attention of the Jūden-chan, who target her charged emotional state.

Later developments grant her the capacity to detect and engage with Jūden-chan, mirroring Sento’s unique ability. This evolution intertwines her personal journey with the story’s supernatural threads, though her core arc remains rooted in reconciling unresolved affections and self-discovery. Allies like Plug Cryostat intervene strategically, leveraging her emotional ties to mediate between human and parallel-world dynamics, subtly expanding her role beyond personal longing. Her narrative persists as a blend of intimate vulnerability and gradual empowerment within the series’ broader mysteries.