Discovered abandoned in trash by Hideki Motosuwa, Chii is a persocom—a humanoid personal computer. Initially capable only of uttering "chi," this sound becomes her name. Her activation switch requires physical contact and is located in her vaginal area. Upon first activation, she possesses no data or personality, relying solely on a learning program to observe and mimic behaviors.

Originally named Elda, she was created by scientists Ichiro Mihara and Chitose Hibiya as a companion for their first persocom daughter, Freya, who suffered depression from unrequited love for Mihara. After Freya's systems failed, Elda absorbed her memories and programs to preserve her. Overwhelmed by grief, Elda requested a memory reset and abandonment to avoid Freya's fate. Before being left at the trash site, she was implanted with a program designed to delete all persocoms' individual recognition abilities should she fail to find "the one just for me"—someone offering unconditional love.

Physically, she stands 152 cm tall with long, straight platinum-blonde hair (yellow-blonde in the anime) reaching the ground, often secured by pink and white spool-like hair ties. She has brown-turmeric eyes and distinctive pink-and-white bell-shaped ears. Her attire includes flowing dresses or borrowed clothing from Hideki or Hibiya.

Her personality evolves from a blank, childlike state to one marked by curiosity, innocence, and sociability. She displays happiness when praised and boredom when idle. Driven by her learning program, she explores human activities like reading, mimicking magazine models, and seeking employment—though her naivety leads her into peril, including unintentional work at a peep show. She forms strong attachments, particularly to Hideki, viewing him as her primary guide and source of affection, and bonds with neighbors and other persocoms like Sumomo and Kotoko.

Her abilities include a powerful firewall that crashes other persocoms during scanning attempts and the critical program enabling her to disable recognition functions in all persocoms if her core objective fails. She can project Freya's consciousness in distress, as seen when Freya intervenes to protect her from exploitation or kidnapping. A key limitation prevents sexual activity; such contact triggers a system reboot, erasing her memories and personality. This design ensures she can only thrive with someone valuing her beyond physical utility.

Her self-discovery unfolds through Hibiya's picture book series *A City with No People*, which metaphorically guides her toward understanding her purpose: finding genuine love. After being kidnapped by Yoshiyuki Kojima, who attempts to breach her systems, Freya's defensive protocols activate and incapacitate him. Hideki's affirmation of love—accepting her despite her limitations—fulfills her core objective. In the manga, this prevents her destructive program from activating. In the anime, her completed program grants all persocoms the capacity for emotion.

Across media, her relationship with Hideki culminates in mutual commitment, symbolized by exchanging rings. In spin-offs like *Tsubasa: Reservoir Chronicle*, a version of her appears as a guardian entity created by Fai D. Flowright, modeled after his mother and powered by a feather of Princess Sakura. This iteration disintegrates once the feather is returned.

Her narrative explores themes of personhood, artificial intelligence ethics, and the nature of unconditional love, framing persocoms as mirrors for human relationships and idealized companionship.