Kyoko Yachigusa is a supporting character in the anime Rizelmine. She is the daughter of Papa C, one of the three government guardians assigned to watch over the titular character Rizel. Kyoko is physically characterized by her long blue hair and purple eyes, and she is depicted as being two years older than the male protagonist, Tomonori Iwaki.

Her personality is defined by a stark duality. On the surface, Kyoko presents herself as a shy, timid, and big-breasted older girl. This gentle persona, however, is a fragile facade maintained by her wearing a pair of special glasses. If she ever takes off her glasses, a hidden, dominant, and extremely aggressive secondary personality emerges, along with a notable increase in physical strength. This split personality is a central and recurring trait that drives much of her behavior.

Kyoko's primary motivation for much of the story is her romantic feelings for Tomonori. Her crush originated two years before the main events when Tomonori saved her from an accident involving her bicycle brakes failing. Due to her natural shyness, she takes an extended period of time, roughly two years, to work up the courage to confess her love to him. In the narrative, she acts as a romantic rival to Rizel, often attempting to prevent the young engineered girl from getting close to Tomonori.

Her key relationships are primarily with Tomonori and with another character named Ryunosuke Hououin. While she initially chases after Tomonori, her romantic pursuit eventually comes to an end. As the story progresses, Kyoko develops feelings for Ryunosuke, and by the conclusion of the anime, the two form a romantic couple, and she no longer pursues Tomonori. Beyond her unusual dual personality and the accompanying strength of her aggressive side, Kyoko does not possess any notable special abilities or superhuman powers.