Lemon is a twelve-year-old orphan girl rescued by protagonists Cacao and Parfait during their mission aboard the invading spacecraft Giga Genos. Freed from captivity alongside other children, she joins their quest. Her name functions as a pun referencing explicit content in anime and manga terminology.

She quickly becomes a companion to the main characters, displaying mischief through interactions with advisor blob PQ. She frequently subjects PQ to physical abuse—throwing, stretching, or stepping on him—establishing her as a playful yet occasionally antagonistic figure.

Her orphan background remains unexplored, with her initial purpose centered on aiding Cacao and Parfait against the antagonist posing as Ramunes IV. Her involvement escalates during the climax when the Dark Knight mecha runs out of control. Unexpectedly, the Dark Knight recognizes Lemon as the legitimate Fourth Warrior Ramunes, rejecting the impostor. She halts the mecha's rampage with a command, saving the planet.

Following this pivotal role, a post-credits sequence teases a sequel titled "Knights of Lemon," implying potential future adventures centered on her. No such sequel was officially produced or released. Visual media, including ending sequences, occasionally portrayed her in a sexualized manner despite her childlike appearance, contributing to controversy.