Lily is a young girl living in the future dimension known as La'cryma. She is the seven-year-old daughter of Miho Mukai, who is blind in this timeline. Because of her mother's condition, Lily acts as her eyes, helping her navigate their world. Lily physically resembles her mother closely, but her demeanor is noticeably more cautious and suspicious, especially toward strangers.

Her role in the story begins when Haruka Kaminogi arrives in La'cryma and asks for a route to the surface. Lily provides directions and later finds a safe place for Haruka and Yuu Gotou to hide when the Dragon Knights are pursuing them. Despite her wariness, Lily shows a willingness to assist those in need, likely influenced by her close bond with her mother and the harsh realities of La'cryma's underground existence.

Lily does not undergo significant character development within the series; her presence serves primarily to illustrate the conditions of life in La'cryma and to offer practical aid to the protagonists during their time in that dimension. Her notable abilities are limited to her knowledge of the local geography and her role as her mother's guide, which requires attentiveness and resourcefulness for a child her age.