At an undetermined period, Aced became one of the apprentices of the Master of Masters, alongside Ava, Gula, Invi, Ira, and Luxu. He was given a Keyblade forged from his own heart by the Master of Masters, and eventually achieved the rank of Keyblade Master himself.
Sometime after, Aced was assigned as the leader of the Ursus Union and was given a copy of the Book of Prophecies. He, alongside four of the five apprentices, was tasked with the collection of Lux by defeating the Heartless in several worlds. In addition, Aced was also introduced to the Chirithy, a Spirit created by the Master of Masters to guide and aid Keyblade wielders. In time, Aced was personally instructed by the Master that in the event of him disappearing, Aced would have to support Ira as their new leader. Upon being informed that Ira's leadership may be challenged one day, and that he must step forward when such a thing happens, Aced accepted the role given to him.
The Master of Masters eventually disappeared, and the Foretellers met again at the behest of Ira, who both announced his belief that a traitor existed amongst the Foretellers, giving the appearance of a Nightmare Chirithy as his proof, upon which Aced immediately proclaimed his innocence. The usage of the special bangles that allowed the Union members to collect dark energy was used by Ira to back his belief of a traitor in the Foretellers, claiming that only one of them could have acquired such an item. Aced backs Invi when she disagreed with Ira's accusation, questioning both the association of the bangles to the power of darkness and that of the Nightmare Chirithy's involvement, then blaming Ira for having cast the seeds of doubt amongst the five Keyblade masters.
As seen in the epilogue, Ace and the other foretellers, excluding Ava, were summoned by Xigbar, who survived the Second Keyblade War, retrieves Xehanort's Keyblade, and revealing himself to be an incarnation of their fellow Keyblade apprentice, Luxu. Upon his arrival, he angrily questions Luxu about the events that had occurred, and what was Luxu's role.