Yui Yamada is the narrative's main protagonist. A dedicated member of her school's greenery committee, she passionately tends plants and flowers on the grounds. She has pale skin, shoulder-length blonde hair often featuring front bangs she once accidentally cut too short, honey-colored eyes, and rosy cheeks. Her standard attire is her school uniform: a short-sleeved white shirt with a small red ribbon, a beige vest, and a red-orange checkered skirt. For gardening, she typically dons a straw hat with a pink ribbon and an orange garden apron. Outside school, she prefers cute, casual clothing. Physically petite, she stands shorter than her romantic partner, Tomoka Kase.

Initially timid, shy, and reserved, Yui exhibits nervousness in social settings, self-doubt about her worth, and difficulty asserting herself, often becoming overly accommodating. Before her relationship with Kase, she had few friends, with Mikawa as her sole close companion. Her personality blends kindness, responsibility, and diligence with anxiety, jealousy when others interact with Kase, and occasional overthinking. She experiences intense emotional reactions, crying from happiness upon learning Kase wants to see her during summer break and becoming flustered when Kase visits her home. She also displays covert perverted tendencies, losing sleep after seeing Kase undress due to fantasizing.

Yui secretly admires Tomoka Kase, initially believing she lacks opportunities to connect. Their relationship begins when Kase starts helping water plants, leading to conversations where mutual feelings surface—Kase had similarly admired Yui. Their romance progresses through multiple kisses and instances of sleeping together. Yui frequently daydreams about their future, including marriage and adopting Kase's surname. Challenges arise, including Yui's jealousy over Kase's interactions, communication difficulties stemming from Yui's reluctance to express her needs, and differing intimacy approaches. During a school trip to Okinawa, Yui avoids joining Kase in the hot springs due to embarrassment about being seen naked, causing temporary tension resolved through open communication.

After high school graduation, Yui initially plans literature studies at her mother's alma mater but switches to horticulture at a Tokyo women's university upon learning Kase received a sports scholarship to a Tokyo university. This decision, driven by her desire to stay near Kase, involves overcoming parental disapproval. In college, she begins forming independent friendships for the first time, marking personal growth. Despite ongoing shyness, she gradually gains confidence within the relationship. She and Kase eventually move in together, continuing their partnership while navigating university life and future aspirations. Her favorite candy flavor is strawberry, and she enjoys fluffy items. She dislikes her singing voice, recognizing it as a weakness.