Lemon Yamagishi begins as a 13-year-old transfer student from St. Marie Academy's Paris main campus to its Japanese branch. A talented but fiercely competitive patisserie student, she displays manipulative tendencies during the Cake Grand Prix by deliberately misleading Ichigo Amano to use unboiled kiwis—exploiting Ichigo's culinary inexperience to sabotage her dessert. Driven solely by victory and viewing peers as rivals, Lemon suffers a major setback after losing the competition. This defeat prompts her return to Paris, where she commits to refining foundational skills and overcoming her self-centered attitude and poor sportsmanship.

Over two years, Lemon matures significantly. At 15, she skips a grade through academic excellence and rejoins St. Marie's Japanese campus as a first-year high school student, now sharing Ichigo's grade level. Her personality transforms: she grows respectful and humble, openly admiring Ichigo as a role model, addressing her as "senpai," acknowledging past misdeeds, and extending genuine friendship instead of rivalry.

In subsequent events, Lemon becomes a core member of the reformed Team Ichigo. She collaborates with Ichigo, Makoto Kashino, and Johnny McBeal on Henri Lucas's professional patisserie shop venture, contributing her refined skills and cooperative spirit. Her long-term goal evolves into establishing an elegant café for affluent patrons, reflecting her growth into a community-focused patissiere dedicated to spreading joy through confections. Physically, she has blonde hair often tied in pigtails or Chinese buns during baking, green or olive eyes, and a fair complexion. Her sweets spirit partner is Mint, who accompanies her journey.