Chiya Ujimatsu is a central character and classmate to Cocoa Hoto, as well as a childhood friend to Syaro Kirima. Her family runs the Japanese sweets café Ama Usa An, which features a rabbit mascot named Anko. The café was historically a rival to Rabbit House, though the younger generation does not actively maintain this rivalry.

She has long, straightened dark brown hair styled in a manner similar to a hime cut, with distinctively longer and differently shaped forelocks. A flower ornament with a ribbon adorns the side of her head. Her fair skin and gentle green eyes curve downward. She typically wears a dark green kimono with vertical stripes, covered by a long white frilly apron as her work uniform.

Chiya possesses a gentle, calming, and formal demeanor. She is soft-spoken and often maintains a light, airy mood, focusing on keeping peace among her friends. Though generally kind, she can be somewhat air-headed and has several surprising quirks that contrast her ladylike exterior. She enjoys giving elaborate and fancy names to the sweets at her family's café, such as "Red Jewel in a Snowy Field" and "Moon and Stars Reflected Upon the Sea." She also has a fondness for scary stories and occasionally unsettling others. She dreams of becoming a samurai and is known for her teasing nature. Despite her calm disposition, she tires easily from strenuous activity but displays an uncanny ability to avoid objects thrown her way.

She quickly became close friends with Cocoa after meeting at school. Her longest friendship is with Syaro Kirima, her childhood friend and neighbor. She felt hurt when Syaro once stated she had no intention of working at Ama Usa An in the future, though Chiya still hopes they will work together someday.

The historical business rivalry existed between her grandmother and the grandfather of Chino Kafū, who founded Rabbit House, but there is no indication that she or Chino intend to continue this competition.

Her name, Ujimatsu Chiya, is a pun on "Uji Matcha," a high-quality green tea from the Uji region. The characters in her given name, Chiya (千夜), can also be interpreted to mean "a thousand nights."

She demonstrates proficiency in acting, as noted in anecdotal accounts from others within the story.