imaginative-ink:

I’ve had this long-standing theory that Isa figured out Xehanort’s true intent for Organization XIII a long time ago, but never told Lea. Instead, he allowed himself to become a vessel in hopes of tearing Xehanort’s plan down from the inside, and to ensure that Lea wouldn’t suffer the same fate. Or perhaps Xehanort made Isa some promise that he’d leave Lea alone if Isa gave himself up (it seems that Xehanort knows of Isa and Lea’s past since he orders Isa to attack Lea in DDD). Anyways, once Isa became a vessel and got a permanent Recusant’s Sigil, Isa cut off all ties with Lea so that Xehanort could never use him as leverage. Not to mention that the two of them were still (sort of) working together on their secret plot, and they couldn’t risk Xehanort finding out about it. 

Now that they’re human again and Lea is a possible candidate to be a Guardian of Light, the part of Isa still untouched by Xehanort – small as it is – becomes more desperate to protect the one friend he’s ever known.