Echoes is an alien entity who arrives on Earth with the purpose of evaluating humanity. He takes on a human form that is described as being highly evolved, appearing as a young man with gray shoulder-length hair and yellow eyes. A significant limitation imposed on him is that his ability to communicate is restricted to only repeating the words spoken by others around him, which is the reason for his name, referencing the Greek nymph Echo. The name also serves as an allusion to the Pink Floyd song from the album Meddle, fitting a series pattern of naming characters after Western music.

Upon coming to Earth, Echoes was captured by the Towa Organization, a group that misunderstood him to be a mutant human. Through studying him, the organization was able to create their synthetic humans. They also attempted to create a clone of Echoes, but this effort was imperfect. The clone, which was more than human but had to eat people to survive, became known as the Manticore and was considered a monster. When the Manticore escaped from the laboratory, Echoes gave chase, feeling a responsibility to stop the creature that was created from him.

The story of Boogiepop and Others finds Echoes disheartened and disillusioned with humanity as he searches for the Manticore. He collapses in the middle of the city, where he is found by Boogiepop, who offers him encouragement and protection from mistreatment by the police. After this encounter, Echoes meets a high school student named Naoko Kamikishiro. The two share a telepathic link that allows her to understand him despite his inability to form his own sentences, and she learns about his origin, his mission, and his suffering. Showing him great compassion, she shelters him at Shinyo Academy and seeks help from her friend, Nagi Kirima.

Echoes’s role in the story is that of an outsider whose judgment of humanity hangs in the balance. His experiences with cruelty and indifference could lead him to a negative conclusion, but the kindness shown to him by a few individuals, particularly Naoko, becomes a pivotal factor. His key relationships are central to this arc. Boogiepop provides the initial push he needs to continue, and Nagi Kirima works to protect him. However, his connection with Naoko Kamikishiro is the most significant; it is suggested that the compassion she showed him was what saved humanity from his judgment. His enemies are the Manticore and a student named Masami Saotome, who becomes an ally to the creature. In a moment of betrayal, Saotome stabs Echoes through the throat with a poisoned mechanical pencil, weakening him so that the Manticore can attack.

In his development, Echoes moves from a state of despair to one of decisive action. Though he is initially defeated by the Manticore, he finds the strength for a final, powerful act. For the only time, he speaks his own words rather than repeating those of another, saying, "my body into information, transmit to source". Upon uttering this phrase, his body transforms into a pillar of light that passes through his enemies, disintegrating Masami Saotome and mortally wounding the Manticore. This self-sacrificing act represents the culmination of his journey, transforming his perceived weakness into a force that saves others. His perspective throughout the narrative serves to illustrate themes of unjust prejudice and the insensitivity of modern society toward the unfortunate.