Even and Ienzo knew each other through being apprentices of Ansem the Wise. Ienzo was orphaned for unknown reasons so Ansem took him in. However, it was often Even who watched over him. Ienzo was supposed to stay inside of the castle but disobeyed orders and went outside. He was surrounded by unversed until a boy named Ventus came by to save him. Even eventually caught up and thanked Ven while explained Ienzo's past to him. Eventually, Xehanort turned the both of them into heartless.
When Even and Ienzo were turned into heartless, they both also created nobodies. Xemnas recruited them into Organization XIII and named them Vexen and Zexion respectively. The two often worked together. They were eventually sent on a mission to Castle Oblivion. They consulted with each other once Riku entered the castle. Vexen and Zexion also investigated Marluxia after learning that he was planning to take over the organization. Vexen is killed by Axel in order to get to Marluxia which causes Zexion to distrust him. Zexion is eventually absorbed by the Riku Replica. Even and Ienzo later become whole again and wake up in Radiant Garden. Ienzo wakes up while Even remains unconscious.
VekuZeku was once a very popular Kingdom Hearts ship. It was popular until it was revealed that Ienzo is a lot younger that Even which disgusted many fans. However, Zexion seemed to age as a nobody while in the organization and was grown up when he reappeared as Ienzo. A lot of fans now ship Zexion with Lexaeus and this pairing often rivals VekuZeku.
- The Riku Replica was created by Vexen and he ironically ended up killing Zexion.