Lilli is a mischievous fairy imprisoned within a book as punishment for excessive pranks. She gains freedom when shy Tiko receives the book as a birthday gift and opens it. To integrate into human life, she uses magic to alter the memories of Tiko's family, convincing them she is Tiko's long-lost twin sister. This false identity allows her to live with them permanently.

Her core personality centers on playful trickery, particularly targeting Hina, Tiko's younger sister, though her antics gradually mellow while retaining a mischievous streak. She employs magical incantations like "Maharu Tamara Furanpa" to cast spells, solving everyday problems or enabling whimsical scenarios. Her adjustment to human family dynamics and mundane life is a significant fish-out-of-water experience.

Her character develops through her deepening bond with Tiko and the family. Initially focused on pranks, she gradually embraces her household role. A notable incident involves accidental intoxication after consuming whiskey during a cooking attempt with Tiko, leading to chaotic magic and property damage. This episode highlights her adaptation challenges.

Her story concludes when she reveals her magic to save her adoptive mother from a knife accident. Faced with returning to her realm, she chooses to remain with the family after Hina destroys the book serving as her portal home. This act permanently severs her magical abilities, finalizing her transition to ordinary human life and solidifying her familial bonds.