Yui Hanasaka is a 17-year-old third-year high school student from Hokkaido who relocates to Tokyo to take her university entrance exams, temporarily residing with her older sister. She has shoulder-length black hair with a clover pin on each side, square bangs hanging on the left, and yellow eyes touched by a slight black tint.

An outgoing, supportive, generous, gentle, and loving person, she befriends a university student neighbor shortly after moving in and asks him to help her prepare for the admission exams to his university. Their bond deepens as they share special days together, leading them to fall in love. As university students and lovers, their relationship encounters challenges, including arguments and insecurities, but these trials ultimately fortify their connection.

The couple transitions into working adulthood, a significant turning point in their lives, and eventually marry. Yui Hanasaka gives birth to a daughter. A new project revisits the story from the second season and explores the third season's events, featuring new monologues that provide insight into Yui's emotions and perspective.