Lillie is a student at the Pokémon School on Melemele Island in the Alola region, where she becomes a classmate and close friend of Ash Ketchum. She is a gentle and reserved girl with a deep love for Pokémon, though she initially suffers from a crippling fear of touching them. This phobia stems from a traumatic incident in her early childhood, when an Ultra Beast known as Nihilego attacked her and she was rescued by a Type: Null, which later evolved into Silvally. The memory of the attack was repressed, leaving her unable to physically make contact with any Pokémon without panic. Despite this fear, Lillie possesses extensive knowledge about Pokémon and devotes herself to studying them from a safe distance, often reading or observing them in the enclosure she maintains at her home.

Her primary motivation throughout the series is to overcome this fear and grow more confident in her own abilities. She also seeks to understand her family’s troubled history, particularly the actions of her mother, Lusamine, the president of the Aether Foundation, and her older brother, Gladion. Lillie’s role in the story expands as she becomes an active participant in the Pokémon School’s adventures and later joins the Ultra Guardians, a team formed to handle Ultra Beast incidents. She cares for a Pokémon Egg entrusted to Professor Kukui, which hatches into an Alolan Vulpix she names Snowy. Snowy’s timid but loyal nature mirrors Lillie’s own, and their bond helps her take the first steps toward touching and battling with Pokémon.

Key relationships shape Lillie’s development. Her friendship with Ash encourages her to face challenges head-on. Gladion serves as both a protective older brother and a mentor, helping her piece together her lost memories and ultimately reconcile with Lusamine. Her relationship with Lusamine is complex, marked by love, fear, and eventual understanding as Lillie learns about her mother’s obsession with Ultra Beasts and the cost of her actions. By the end of the series, Lillie fully recovers her memories, overcomes her fear, and becomes a confident Pokémon Trainer capable of using Z‑Moves, notably the Subzero Slammer with Snowy. She also discovers a dormant Magearna in her father’s old office, which later awakens and helps guide her to her missing father.

Throughout the anime, Lillie’s growth is gradual and emotionally driven, moving from a girl who shied away from any physical contact with Pokémon to a determined trainer who actively battles alongside her friends and protects others. Her intelligence, empathy, and quiet resilience make her an essential part of the Alola group’s journey.