Yui Hanasaka is a 17-year-old high school student from Hokkaido who relocates to Tokyo to focus on her university entrance examinations, temporarily residing with her older sister. She has shoulder-length black hair fastened with a clover pin on each side and square bangs that fall across the left side of her face. Her eyes are yellow with a subtle black tint. Shortly after moving into her new apartment, she encounters her neighbor, a university student attending the institution she hopes to enter. She asks him for help preparing for her admission exams, and he agrees. Their connection deepens through study sessions and the time they share. Yui possesses an outgoing, supportive, generous, gentle, and loving nature. She is neat and earnest, applying diligent effort to everything she does. Her relationship with the protagonist evolves beyond academic tutoring into romance, continuing through their university years and into their professional lives. As a couple, they navigate disagreements and personal doubts, each challenge serving to fortify their bond. A significant transition occurs as they enter the workforce. In the official narrative, Yui eventually marries the protagonist and they have a daughter. Her story is revisited in the visual novel "One Room -Hanasaka Yui Memorial-", which covers events from the second season and expands into the third season, focusing on her adult life. The meaning of her name comes from its Kanji components: her surname Hanasaka combines "flower" (花) and "slope" (坂), suggesting "hill of flowers," while her given name Yui combines "tie" (結) and "garment" (衣).