In the anime Himitsu no AiPri, the character known as Chii is Chii Mamiya. She is a supporting character who attends Paradise Private Academy alongside the main cast and is a classmate of the protagonist Himari Aozora and the cool and serious idol Mitsuki Hoshikawa, whom she considers her rival.

Chii possesses a vibrant and determined personality, carrying herself with a confident and even boastful demeanor. She is a self-described go-getter who is not afraid to assert that she is the best, and she has a deep love for rock music, which heavily influences her energetic performances. Despite her outward bravado, Chii often feels that other characters do not take her ambitions seriously, reacting to her claims with indifference rather than recognition.

This tension between her public confidence and private insecurity forms the core of her motivations and character arc. Chii is driven by a genuine desire to be the brightest star in the AiPri world, known as the AiPriVerse. However, this determination makes her vulnerable to self-doubt, particularly when it comes to measuring her success against others. She becomes trapped in the habit of constantly checking the AiPri rankings to see if she has placed higher, a relatable struggle that reflects a need for external validation. This feeling of being overshadowed is most acute in her relationship with her friend, Tsumugi Suzukaze. While Chii genuinely values Tsumugi as a friend, she cannot help but feel envious and outshined by Tsumugi's natural radiance and success, leading to a painful internal conflict.

Chii's role in the story is significant as she experiences a notable character transformation driven by these negative emotions. Her envy and frustration culminate in a dramatic event when she finally voices her feelings of being outshone. In response, a dark power emerges from her AiPri Bracelet, creating a malevolent entity known as Dark Chii. This shadowy duplicate takes on Chii's form and goes on stage to imprison Tsumugi, an act for which the real Chii is initially blamed. This incident highlights Chii's internal struggle and serves as a physical manifestation of her darker impulses.

In terms of her abilities as an idol, Chii is known for her energetic and distinctive performance style. She performs the song Gira Gira Star, which is noted for being an upbeat and fun rock-influenced track that stands out from other performances. Her abilities are a direct expression of her personality, channeling her passion and drive into her live shows.