The Girl from Angel's Egg is an unnamed young protagonist who wanders alone through a desolate, post-apocalyptic landscape. She appears as a prepubescent child with delicate features, voluminous white hair, and pale skin, dressed in layered skirts of soft pink and lilac along with a bright shawl, making her the only source of warm color in the otherwise grey and shadowy world she inhabits. Her entire existence revolves around the protection of a single, large, mysterious white egg that she carries with her at all times, often hiding it beneath her clothing. The Girl believes the egg was laid by an angel and is dedicated to keeping it safe and warm, nurturing it with the hope that it will one day hatch and usher forth a new beginning or a better world.

Living as a scavenger in a ruined neo-Gothic city, her daily routine consists of hunting for food, water, and various glass bottles and artifacts amidst the rubble. She navigates this eerie environment with a profound sense of wariness, especially avoiding the spectral, faceless soldiers who mindlessly hunt the shadows of giant fish, a futile act that underscores the lingering, purposeless rituals of this dying realm. The Girl embodies a sense of pure, unquestioning faith and hope. She does not know for certain what the egg contains, nor does she seek to know; her purpose is derived from the act of protecting the potential it represents. Her personality is initially defined by a quiet, introverted determination and a deep-seated distrust of the unknown, which manifests as fear when she first encounters the Boy, a mysterious wanderer who carries a large, cross-shaped weapon.

The central relationship in the narrative is between the Girl and this unnamed Boy. Their dynamic drives the film's thematic exploration of faith versus doubt. Initially, the Girl tries to flee from him, but he persistently follows her, and a tentative bond forms. The Boy, who represents a more cynical, questioning, and perhaps spiritually bereft perspective, challenges her directly by suggesting they break the egg to discover what is inside, a proposal that horrifies her. Despite her fear, she begins to trust him, leading him to her hidden sanctuary within a beached, ship-like structure and showing him the fossilized skeleton of an enormous angel in an underground cavern, which she believes is the parent of the creature within her egg. The Boy responds by telling her a fatalistic version of the biblical story of Noah's Ark, where the dove never returns, implying a world abandoned by God and devoid of a future.

The Girl's arc is tragic and pivots on a single, devastating act of betrayal. After she falls asleep, the Boy takes her egg and smashes it with his weapon, revealing it to be empty. This act represents the violent shattering of her faith and purpose. Upon waking and discovering the broken shell, she lets out a silent, heartbroken scream and rushes out to confront him. In her frantic pursuit, she falls from a cliff into a deep body of water. As she drowns, her form briefly transforms into that of an adult woman, and her final exhaled breath rises to the surface as a multitude of new, intact eggs. Her death is not presented simply as an end, but as a dissolution and transformation. In the film's final moments, the massive, orb-like vessel that had descended at the beginning of the story rises from the ocean, its surface now adorned with a new stone statue: the Girl, sitting serenely on a throne, once again holding her egg. While she possesses no supernatural abilities in a conventional sense, her notable characteristic is her profound dedication to the egg and her capacity for unwavering hope and faith in the face of absolute desolation, a quality that gives her a ghostlike, ethereal presence as though she might dissipate at any moment.