Chiko Sekino, a third-year middle school student, leads the idol group Cream Anmitsu while navigating a complex bond with her older sister, Roko Sekino—a former child actor and member of rival group Fruit Tart. Though three years Roko’s junior, Chiko stands 24 centimeters taller, a physical contrast she leverages to playfully infantilize her sister, masking her own mature exterior with teasing antics. Her childhood idolization of Roko once drove her to replicate her sister’s hairstyle, later adjusted to a distinctive side bun with square bangs as a mark of individuality. This devotion deepened into a sister complex, evident in her habit of recording Fruit Tart’s broadcasts solely to rewatch Roko’s segments, sleeping with a Roko-inspired plushie, and initiating affectionate yet possessive gestures like spontaneous hugs or playful groping. She further supports Roko covertly by voicing a character in her sister’s cherished cartoon, a secret she guards closely.

Balancing idol responsibilities with swimming and voice acting, Chiko thrives as Cream Anmitsu’s center, her leadership tempered by discreet vigilance over Roko’s well-being. Her style blends whimsy and sophistication: waist-length plum hair cascades into a side bun, paired with a violet checkered shirt, red tie, midnight blue skirt edged in white, black stockings, and crimson shoes.

The surname "Sekino" anchors her ties to Tokyo’s Koganei City, specifically its Sekino-cho district, part of a narrative tradition linking characters to local landmarks. Her birthdate follows the series’ "Iroha" poem framework, aligning numerically with her debut order. Publicly poised, Chiko’s private dynamic with Roko oscillates between affectionate dominance and quiet vulnerability, her actions driven by a resolve to preserve their connection amid the rivalries of their idol worlds.