C-ko Kotobuki, legally named Shiiko Kotobuki, is a blonde-haired individual radiating a childlike demeanor marked by hyperactive energy and a habit of referring to herself in the third person (in Japanese contexts). Her personality blends wide-eyed innocence with bouts of immaturity, frequently erupting into tears or selfish demands, particularly in her clingy devotion to childhood friend A-ko. This bond, rooted in shared experiences since kindergarten, skews toward platonic hero worship rather than romance.

Born the Fourth Princess of the Fifth Queen of Alpha Cygni’s all-female Lepton Kingdom, her extraterrestrial origins contrast with her Earthbound life. After crash-landing as an infant, she was adopted—first by a mother in one timeline, later by a father leading Kotobuki Industries following her mother’s death in another. Though royal by blood, she dismisses her alien heritage, clinging to her mundane existence with A-ko.

In *Project A-ko 3: Cinderella Rhapsody*, her jealousy erupts when A-ko pursues romance with Kei Yuki, driving C-ko to snarl and hiss at Kei with feral intensity. After Kei confesses his love, she rebuffs him, doubling down on her loyalty to A-ko. This arc underscores her role in igniting conflicts between A-ko and rival B-ko, though her actions stem solely from desperation to preserve her primary relationship.

Alternate continuities, like *A-ko the Versus*, reimagine her as a 10-year-old industrialist heiress while retaining her innocent, dependent core. Comedic quirks include cooking disasters featuring alien-grade ingredients and hobbies like curating dolls or binge-watching films with A-ko.

Across narratives, she anchors A-ko emotionally, driving tension through naivety that attracts others’ obsessive agendas—from B-ko’s rivalry to her alien kin’s attempts to reclaim her. Yet her focus remains unshakable: defending her earthly ties against all interference.