Noriko Kawada is Keiichiro's deceased younger sister, killed in a traffic accident three years before the main events. Her death occurred during a family trip to one of Keiichiro's live band performances, profoundly deepening his grief and prompting his withdrawal from music.

She cherished Italian white sunflowers, a detail that gains symbolic weight when Keiichiro discovers an abandoned android named Flower clutching an identical sunflower. This visual echo sways his initial impulse to discard the android, compelling him to bring her home instead.

Noriko exists solely through Keiichiro's memories and lingering sorrow, never appearing directly in the narrative present. Her absence anchors his character background, fueling his emotional detachment from the world. Flower's discovery and her sunflower subtly invoke Noriko's memory, forging a thematic bridge between Keiichiro's unresolved trauma and his evolving bond with the android.

Her role remains confined to Keiichiro's history, with no documented expansion into additional backstory, alternate seasons, spin-offs, or other media narratives.