Itsuka Yukihira is a ten-year-old girl living and working at Ryokushō, the Irino family's traditional wagashi shop in Kyoto. She arrived there roughly one year before the story's start, abandoned during heavy snowfall by her father, Tomoe Yukihira. Her mother, Shinri Yukihira, had also previously left her, scarring her emotionally and instilling a deep fear of further abandonment.

She has light brown hair, usually tied up, and brown eyes. While working, she wears a Japanese waitress uniform daily. Despite her youth, Itsuka displays a strong work ethic, maturity, and professionalism. She believes children must shoulder responsibilities equal to adults, a mindset stemming from her father's dismissive remark that "children are useless." This drives extreme self-reliance; she avoids inconveniencing others and initially struggles to accept support.

Her relationship with Nagomu Irino, the son of Ryokushō's owners, is central. Initially, she views him with contempt due to his clumsy work ethic, perceiving him as unserious compared to her disciplined approach. Determined to inherit Ryokushō, she openly declares she will not relinquish this position to Nagomu, whom she considers unworthy. However, Nagomu's consistent efforts to connect with her—like supporting her during a prank order crisis by performing music to sell excess sweets—gradually soften her stance. Their bond evolves into a surrogate familial relationship, with Nagomu functioning as a supportive older brother or guardian figure due to their age proximity.

Itsuka harbors deep resentment toward her biological parents for abandoning her. Her father's departure is later revealed as protective: Tomoe fled his own abusive father, who used violence to control the family, believing leaving Itsuka at Ryokushō offered safety and stability. During Christmas, her mother Shinri attempts reconciliation by sending gifts and requesting a meeting. Though wary due to past broken promises, Itsuka agrees to spend time with her mother, indicating tentative steps toward healing, facilitated by her growing security within the Irino household.

Itsuka's development centers on learning to trust others and embrace emotional vulnerability. Early on, she frequently visits the train station hoping to find her father, but eventually stops, symbolizing acceptance of her new life. Interactions with the Irino family and shop employees help her rebuild faith in commitments, exemplified when she and Nagomu make a pact to celebrate her March birthday together—a promise she begins to believe in despite fears of disappointment. She emerges from isolation, finding belonging within the Ryokushō community while maintaining her resolve to inherit the shop.