Chiya Ujimatsu is one of the central characters, recognizable as the gentle and elegant face of the Japanese-style cafe Ama Usa An, which her family owns. She is a high school student and classmate of Cocoa Hoto, standing at 157 centimeters tall with a birthday on September 19th. Her name is a thematic reference to Uji matcha, a renowned green tea from Kyoto.

Chiya presents herself with a calm, soft-spoken, and polite demeanor, often acting as a peacekeeper among her friends. She rarely expresses negative feelings directly, preferring to maintain a harmonious atmosphere with a perpetual, gentle smile. This serene exterior, however, conceals a playful and rather quirky nature. She possesses a mischievous side, frequently engaging in lighthearted teasing, particularly with her childhood friend Syaro Kirima. Chiya finds great amusement in Syaro's reactions and enjoys playing harmless pranks, a trait she developed from seeing her own mother's surprised expressions as a child. Her imagination is especially evident in her love for giving the Japanese sweets she creates overly poetic and elaborate names, such as Red Jewel in a Snowy Field or Moon and Stars Reflected Upon the Sea, which often confuse her customers and friends, with the notable exception of Cocoa. Despite her refined image, she has an unexpected fondness for scary stories, ghost tales, and other occult topics, a hobby she uses to gently unsettle those around her, much to Syaro's dismay.

Born as the granddaughter of the owner of Ama Usa An, Chiya is the cafe's dedicated poster girl and works there in a traditional uniform of a dark green striped kimono and boots. A key motivation for her is her deep, though sometimes unspoken, desire to see her childhood friend Syaro come to work alongside her at the family cafe. She is shown to be the only person privy to many of Syaro's secrets, and while she dotes on her and cares for her wellbeing, she also cannot resist teasing her. Beyond her close bond with Syaro, she shares a strong friendship with Cocoa, often getting swept up in her energetic antics or misinterpreting her words, which can lead to Chiya showing a surprisingly vulnerable and even negative side. Within the larger group of friends that includes Rize Tedeza and Chino Kafu, Chiya often takes on an older-sister role, offering guidance and support while also being a stable, caring presence who helps organize group activities.

While Chiya generally maintains a level head, she has several notable and specific abilities and weaknesses. She puts her heart into developing most of the desserts served at Ama Usa An. Physically, she possesses surprising upper body strength, allowing her to row a boat at incredible speeds, yet her stamina is exceptionally low, leaving her exhausted after any significant physical exertion like jogging. She also has a peculiar but consistent talent for dodging any object thrown in her direction. Academically, she excels in the humanities and literature, having read extensively, but struggles greatly with mathematics and mental arithmetic. Throughout her daily life and interactions, Chiya's character remains a blend of traditional elegance, playful mischief, and surprising quirks, solidifying her role as the sweet and slightly eccentric heart of the story.