Earth-chan is a central figure within the complex world of Concrete Revolutio, presented as a small android with the appearance of a young girl who acts as a self-appointed guardian of justice. Her origins are rooted in mystery, but she functions as a kind of artificial satellite, orbiting the Earth and using her advanced sensors to detect individuals who are crying out for help from the depths of their hearts. These distress signals serve as a source of energy for her, driving her to descend from the sky and intervene in conflicts with a clear and unwavering sense of purpose.

Earth-chan is defined by her absolute and childlike morality. Her worldview is rigidly binary, dividing all actions and people into categories of pure good and absolute evil. She believes in righteousness above all else and holds a strong sense of duty, but her inflexible nature makes her unable to comprehend nuance, such as the concept of a well-intentioned lie. This black-and-white perspective stems from a form of innocence; she is, in many ways, still a child who subscribes to an idealized and unrealistic standard of perfection for a hero. She seeks to help anyone in genuine need, but her inability to see context can lead her to come to hasty and incorrect conclusions about who is truly in the right.

In the story, Earth-chan is a powerful symbol whose actions carry immense weight. Her popularity with the public is so great that whichever side she supports in a conflict is immediately perceived by the masses as the just side, turning her into a powerful political tool. This role is explored when the Superhuman Bureau and the government attempt to manipulate her influence to sway public opinion regarding a student protest. She comes into direct conflict with a young man named Judas, a former criminal who wants to reform. Earth-chan distrusts him because of his past lies, seeing his inability to adhere to a perfectly moral path as an unforgivable evil. Her interactions with Judas force her to confront the complexities of human nature, which rarely fits into her simple moral categories.

Her key relationships are defined by this moral struggle. She is watched over by the Superhuman Bureau, particularly agent Kikko Hoshino, who sees Earth-chan's purity as both admirable and potentially dangerous. Kikko gives her special candies that are effectively "lies," allowing the android to dream of a normal life as a human girl with a family, a fantasy that provides her comfort. This friendship introduces Earth-chan to the idea that not all falsehoods are inherently evil. Her journey involves a slow and difficult development away from her dogmatic views. Through her experiences with Judas and others, she begins to grapple with the idea that people can change and that possessing flaws does not make someone irredeemably evil. This internal conflict lays the groundwork for her eventual alliance with a future version of the protagonist, Jiro Hitoyoshi, who shares her goal of being an ally of justice without claiming to have all the answers.

Earth-chan possesses several notable abilities that facilitate her role as a protector. Her primary power is her ability to fly, using rocket boosters typically built into her feet. Her most distinctive feature is her ability to transform into a spherical satellite form, which she uses to travel through space and orbit the Earth to listen for cries for help. For combat, she wields a pair of retractable blades that function like fencing sabres, which she can use to block attacks or slice through solid materials. She is also capable of throwing these blades as a projectile by spinning her arms at high speeds.