Eden Vallock is a young man who investigates war ruins on Mars, though his true purpose for collecting artifacts and technology from these sites remains largely unknown. He is introduced as a researcher with a carefree and lighthearted personality, often appearing whimsical and unpredictable in his interactions. His words and intentions are frequently difficult to decipher, as he maintains an air of mystery about his true feelings and goals. Despite this ambiguous exterior, he occasionally displays a caring and protective side, particularly toward those to whom he feels a close connection.

Eden is a member of the Immortal Nine, a group of powerful beings known as Protoneans, and was originally created by the scientist Roy Junghart. Because of this origin, he possesses the remarkable ability to transform into a formidable combat form known as the Black Noir or Dark Noir. In this transformed state, he takes on the appearance of a sleek, black knight-like figure accented with vivid orange lines and a flowing cape. In battle, he demonstrates exceptional speed and agility, capable of keeping pace with even the fastest combatants. He can convert his forearms into powerful cannons that fire devastating blasts, generate an energy sword for close-quarters combat, and launch massive energy spheres from his chest to destroy multiple powerful enemies at once. His cape is also weaponized, equipped with cannons that can fire in any direction. His endurance is equally extraordinary, as he has survived attacks that manipulate gravity without being crushed.

In the past, Eden fought alongside other Immortal Nine members, including a warrior named Sylvia, in a war against alien invaders known as the Usurpers. After the war concluded, he was invited to join the Alter faction but declined the offer, choosing instead to pursue his own independent research into the secrets of Usurper weaponry. He has a history with several key characters, having once lived alongside a young Jean Junghart, Rouge Redstar, and Naomi Orthmann before leaving them. One of the most significant revelations about his past is his relationship with the scientist Eva Cristella, with whom he was in a romantic relationship. Together, they are the parents of Jean Junghart, a connection that remains hidden for much of the story. Eden carries a photograph of himself, Eva, and Jean, which holds great emotional significance for him.

His role in the story often involves him appearing at critical moments to assist others, such as when he helps Naomi infiltrate a carnival base to rescue Rouge or later saves Rouge and Naomi when they find themselves in grave danger. He demonstrates a particular focus on Jean Junghart, and his actions are frequently driven by motives tied to this relationship. As the narrative progresses, his true identity and paternal connection to Jean are brought to light. At one point, he suffers a severe injury when his core identifier is ripped from his chest, an event that puts him at risk of losing his memories and sense of self over time, similar to a degenerative condition. Even so, he continues to play a role in the events surrounding the Immortal Nine and the conflict between humans and Neans.