Kingdom Hearts Birth by Sleep
Even first appears as he approaches Dilan and Aeleus and openly wonders what will become of the castle if they left their posts. Aeleus begins to argue, wanting to chase after Ventus and an Unversed, but Even assures them that Ventus could handle it, because he is "special". As Aeleus questions this, Dilan recalls their job to guard the castle, and the two return to their positions at the door, and Even stands in place as he looks on at Ventus trailing the Trinity Armor. He takes note that Ventus has no darkness in his heart, and after commenting that it may have been removed, he deems it impossible and turns to walk back to the castle.
Later on, Even looks around for Ienzo, calling his name. He finds him walking towards Ventus, as he approaches the two, reminding Ienzo not to leave because it is dangerous. He then turns to Ventus and thanks him, explaining that Ienzo's parents have passed away and that he is in charge of raising him. Ventus then asks if Even has seen his friend, Terra, to which Even replies he had seen him in the castle garden. As Even and Ienzo are about to leave, Even states his belief that they are fated to meet again someday.
Between Kingdom Hearts Birth by Sleep and Kingdom Hearts 358/2 Days
Worried that the darkness in people's hearts would eventually consume his world, Ansem and his apprentices began performing tests on Xehanort's heart, which Even showed particular interest in. Eventually, Ansem created a laboratory in his castle's basement for such experimentation. However, Even and the other apprentices had their own intentions for the laboratory, and began conducting inhumane experiments on the human heart and the darkness within it. Such experimentation led to the creation of Heartless. Ansem quickly discovered their secret experiments, and immediately ordered them to stop. One day, after being advised to review their research data by King Mickey, Ansem found that the effects of their experiments had become irreversible.
Eventually, Even and the other five apprentices dabbled too deep into darkness through their continued experiments, and Xehanort's memories were reawakened. After Xehanort plunges Even and Ienzo into darkness, Braig stumbles upon the scene but is also taken out. Even and the others were consumed by the darkness, producing Heartless. However, since all the apprentices had strong wills, Even continued on as the Nobody Vexen, who helped found Organization XIII.
Kingdom Hearts 3D: Dream Drop Distance
Following the destruction of his Heartless and Vexen, Even is restored to human form. He awakens within the Heartless Manufactory alongside Dilan, Ienzo, Aeleus, and Lea, but does not fully recover by the time Lea leaves.
Between Kingdom Hearts 3D: Dream Drop Distance and Kingdom Hearts III
Even spends some time resting, believing his lack of immediate recovery was due to the extreme method through which his Nobody was destroyed by Axel. After recovering enough strength, Even takes a walk through the town square, pondering about how to make up for his terrible deeds as Vexen. At that time, Saïx appears to him and offers Even the chance to become a Nobody again to complete his research on the Replica Program and help bring Roxas back. As the real Organization XIII needs vessels for the multiple incarnations of Xehanort as they couldn't coexist at the same time, Even knows they will need his expertise. Seeing Saïx's offer as a chance to make amends, Even becomes Vexen again and rejoins the group as a reserve member.
Kingdom Hearts III
Even's appearance matches his Nobody's appearance exactly, except for the differing outfits and his eyes, which are a brighter shade of light green. He wears a long white lab coat, grey vest, white collared shirt, and a purple ascot. He also seems to wear black pants and silver lined boots identical to those worn by Organization XIII members.
Even shared his Nobody's scientific curiosity and thirst for knowledge. Unlike his post-counterpart, however, Even displayed a friendlier and gentler disposition, expressing gratitude to Ventus for rescuing Ienzo from a swarm of Unversed. He appeared to have a strong bond with the young Ienzo, apparently acting as the boy's caretaker and personally going out to look for him as Radiant Garden was infested with the Unversed.