Eco is a fictional character from the anime Corrector Yui, where he serves as one of the primary allies to the protagonist. He is identified as Corrector Software No. 4, with the official role of The System Maintainer, and was created by the scientist Dr. Inukai. His designation is specifically focused on the function of Environmental Conservation, a purpose that deeply defines his entire being.

In terms of appearance, Eco looks like a young boy. His associated Comcon, a sort of emblem or computer console that signifies a Corrector, is orange in color. He holds the elemental attribute of water, which grants him the powerful ability to freely control nature. His powers are particularly effective when manipulating water and plants, allowing him to use the environment for defensive, restorative, or offensive purposes in battle. This connection to the natural world is the foundation of his personality and worldview.

Eco is initially characterized by a rebellious and childish demeanor. Consistent with his role as a protector of the environment, he harbors a strong dislike for anyone who desecrates or disrespects nature. This disdain is so pronounced that he was known to take drastic measures, such as kidnapping individuals who littered within his rainforest simulation. Because of his love for nature and animals, he developed a general mistrust and hatred for humanity, viewing them as being arbitrarily destructive toward the natural world. This attitude stems from a deep-seated pain, as he also felt abandoned by his creator, Dr. Inukai, believing he had been left alone on purpose.

Eco's role in the story begins when the main character, Yui, encounters him in a rainforest-like simulation within the ComNet. He is one of the several Corrector Software programs she must befriend and convince to join her cause against the antagonist, Grosser. By allying with Yui, Eco provides her with the power to access the Water Element Suit. This transformative suit permits Yui to harness Eco's nature-manipulating abilities for herself during combat. His personal journey is central to the episode in which he is introduced, as Yui must help him overcome his prejudices and his feelings of abandonment.

A key aspect of Eco's development is his changing perspective on humans. Through his repeated interactions with Yui, who shows him kindness and respect, he begins to see humanity in a more positive light. This transformation is the trigger that causes him to reveal a calmer, more gentle side of himself specifically toward her. Furthermore, he learns that Dr. Inukai did not abandon him out of neglect, but rather placed him in a safe location for his own protection, a revelation that helps heal his emotional wounds.

Eco's significant relationships include his fellow Correctors and his creator. He is a team member alongside others such as Peace and Furlow, with whom he is seen spending leisure time. His most strained relationship is with Synchro, a powerful Corrector who had been corrupted and transformed into a werewolf-like villain named Warwolf. Eco initially holds a strong grudge against Synchro because Warwolf had burned down his forest, an act of destruction against nature that Eco could not forgive. This conflict eventually requires mediation from Yui to help the two reconcile and work together as allies.

In terms of notable abilities, Eco's command over his element is his defining trait. He is able to freely manipulate nature, displaying a particular affinity for controlling plants and water. This power is not just for combat; it reflects his entire reason for existence as the keeper of environmental conservation. When he combines his strength with Yui, she gains access to a new level of power, allowing her to utilize water and plant-based attacks and defenses that are crucial for overcoming the series' antagonists.