Lilu features exclusively as a central character in the film "Gekijōban Otoppe Papa Don't Cry," with no appearances in other franchise seasons, OVAs, or spin-offs. She is a baby Otoppe—a creature born from sound—discovered by the Otoppe Windy. Visually, Lilu closely resembles Windy, hinting at a potential familial or species connection, though no explicit biological relationship or origin is established. Windy takes on the role of Lilu’s primary caregiver, serving as her adoptive father figure. This unexpected responsibility drives the film’s core narrative.

Lilu’s arrival in Otoppe Town disrupts daily life, sparking comedic and chaotic incidents among the residents. Her complete dependence on Windy pushes him to navigate parenthood’s challenges, including nurturing, protection, and emotional bonding. These experiences spur Windy’s personal growth, shifting his focus from self-interest to devoted caretaking.

Lilu anchors the story’s exploration of parental love and familial bonds. Her interactions with Windy and the broader community—including fellow Otoppe creatures and the human Sina—highlight collective caregiving dynamics. Though Lilu lacks dialogue or independent development, her influence propels the emotional arc, culminating in the paternal-dedication musical sequence "Papa Don't Cry."

The narrative provides no details of Lilu’s life prior to her discovery, her biological origins, her Otoppe abilities, or her fate beyond the film. Her role remains confined to catalyzing Windy’s journey into fatherhood.