Chinami Noki is a student at the same elementary school as the main protagonists and serves as the vice president of the student council, a role that puts her in a position of authority among her peers. Despite being technically lower in rank than the student council president, Yuriko Ozora, Chinami often behaves as if the opposite were true, taking charge of situations and formulating plans on her own. She is a half-alien spy, possessing cat-like ears and a tail that become visible when she is flustered or emotionally agitated, a trait she shares with her partner, Yuriko. In the story, Chinami initially fills the role of an antagonist, working alongside Yuriko as part of the alien forces attempting to cause trouble for Japan's child defenders, though she is an ineffectual and sympathetic villain, as her schemes are rarely successful.

Chinami is driven by a complex mix of duty and personal feeling. While she carries out her mission as a spy, she is also secretly jealous of Yuriko's carefree and popular personality, as Chinami feels she herself is often overlooked and not given the same attention. This jealousy, however, leads to a moment of self-realization. After being voted Queen of the Beach in a contest, she discovers that she does not actually enjoy being in the spotlight and instead comes to prefer being a supporting character, finding more comfort in a role that is not the center of attention. Her motivations shift dramatically later in the series after she and Yuriko are captured and imprisoned by their own alien superiors as punishment for their repeated failures. Faced with this betrayal, Chinami decides to help Yuriko escape in the hopes that her partner can live a normal life, seeing Yuriko as someone who is genuinely good at heart. When Yuriko refuses to leave without her, both characters make a heel-face turn, abandoning their alien masters and joining the Japanese defense forces to help fight against the other aliens.

Her most significant relationship is with Yuriko Ozora. While Chinami often acts as the more assertive and scheming half of their pair, giving orders and trying to keep Yuriko focused on their mission, she is also deeply protective of her. She frequently has to remind Yuriko that the three main heroines are supposed to be their enemies, as Yuriko genuinely likes them. This dynamic shows that Chinami is often the one who must be pragmatic, even while being the more timid of the two in terms of personality. Her development is marked by a move from being a reluctant or jealous antagonist to a genuine ally, culminating in a decision to rebel against her own kind to save her friend. The series shows that several years after these events, Chinami is working together with Yuriko as a co-owner of a hot springs resort. In this later period, she continues to keep her cat ears hidden, suggesting a continued preference for privacy and a life away from the extraordinary events of her childhood. As a half-alien, Chinami's notable ability is her transformation into a cat girl form, which manifests involuntarily when she experiences strong emotions.