Nino is the mysterious homeless girl who lives under the Arakawa bridge and serves as the main female protagonist of the story. She enters the narrative when she rescues Kou Ichinomiya from drowning in the Arakawa River, an act that creates a debt he feels compelled to repay. When Kou asks how he can settle the debt, Nino tells him to love her, which becomes the foundation of their relationship. She claims to be a Venusian, and this extraterrestrial identity is a central part of her character, though her exact origins remain ambiguous. Her name is derived from the tag on her tracksuit, which reads Year 2, Class 3, or Ni-no-san, which she shortened to Nino.

Nino’s personality is calm, stoic, and childlike in its simplicity. She often forgets important information and relies on Kou to remind her of basic things. When she becomes frightened or angry, she pulls her hood over her head and climbs to the top of a streetlamp. She lives in a cardboard home with a curtain for an entrance and owns a lavish velvet bed, but she chooses to sleep in a drawer underneath it. Her primary motivation is to experience love, and she genuinely seeks a romantic connection with Kou, although her understanding of relationships is unconventional.

Her role in the story is both the catalyst for Kou’s life under the bridge and a steady, grounding presence among the eccentric residents of the Arakawa community. She provides fish for the village by fishing in the river, a task at which she excels because of her remarkable swimming ability. She can stay submerged for several minutes, which allows her to catch fish that others cannot. This skill is one of her most notable abilities and is essential to the community’s survival.

Key relationships include her bond with Kou, which evolves from a debt-based arrangement into a genuine, if quirky, romance. She also interacts with the village chief and other residents, though her connection to Kou is the most developed. Over the course of the series, Nino’s character shows subtle growth as she becomes more comfortable expressing her feelings and trusting Kou. Her background includes a suggested tragic past: according to some accounts, Venusians cannot survive the death of their lover, and Nino’s previous partner died from shock after believing a lie told by the village chief, prompting her parents to send her to Earth to protect her. This backstory adds depth to her otherwise naive and detached demeanor.

Notable abilities include her extraordinary swimming and breath-holding, her fishing skills, and her peculiar habit of perching on high places when stressed. She also exhibits a physical resilience that allows her to live comfortably in a makeshift home under the bridge. Overall, Nino is an enigmatic, gentle, and deeply lonely character whose search for love drives the story’s central relationship.