There is an "X" on it, and who do we know that relates to that? There was an X on Sora's chest as well, and Xehanort used that to track him and eventually turn him into a darkness. Perhaps the same happened with Eraqus. Maybe, at the point where Xehanort "killed" Eraqus, he actually placed one of the pieces of his heart inside of him, like he tried with Sora at the end of DDD, and that light we saw him turn into was actually him going forward in time. We don't know how it looks like when someone does, and most likely Terra really did save a piece of Eraqus just before he disappeared, but Young Xehanort could have been hanging back somewhere, and secretly transported Eraqus to the current present time where DDD takes place to create the illusion of him dying and thus fulling Terra's rage, and made Eraqus one of the thirteen darknesses.
If there's any flaws with this, please point them out. This is just a theory, after all.
Look at his chest...
There is an "X" on it, and who do we know that relates to that? There was an X on Sora's chest as well, and Xehanort used that to track him and eventually turn him into a darkness. Perhaps the same happened with Eraqus. Maybe, at the point where Xehanort "killed" Eraqus, he actually placed one of the pieces of his heart inside of him, like he tried with Sora at the end of DDD, and that light we saw him turn into was actually him going forward in time. We don't know how it looks like when someone does, and most likely Terra really did save a piece of Eraqus just before he disappeared, but Young Xehanort could have been hanging back somewhere, and secretly transported Eraqus to the current present time where DDD takes place to create the illusion of him dying and thus fulling Terra's rage, and made Eraqus one of the thirteen darknesses.
If there's any flaws with this, please point them out. This is just a theory, after all.