Maybe Master Xehanort (after being recompleted) realized that SoD was a heart that conveniently was at Destiny Islands at the time of it falling to the darkness -- so he could enact his plans for 3D with him there -- and also realized that Xemnas conveniently on his own assembled 13 nobodies which he could
Okay so, after looking at DDD again, I think I may have worked out a reasonable explanation for why SoD was on Destiny Islands during it's fall (though how he knew to time travel is still beyond me, lol).
Sora actually asks Young Xehanort, straight up, this exact question, but the only answer given to him was "simple." It's never elaborated on what exactly YX was gonna say, but immediately after he says this, we see an apparition of Kairi. So maybe the implication is that after Apprentice Xehanort cast Kairi out of Radiant Garden, he eventually found her on Destiny Islands and observed her, only to find out she was led to Sora and Riku's light. After this, he would've been present to witness Riku allowing the darkness into Destiny Islands, which would explain why he referenced this exact information to Sora at the end of KH1. Then again, YX also says that when Ansem possessed Riku, he saw all of the boys experiences in real-time, and implies that it was a factor in his time traveling (even if chronologically that would've happened before hand).
If Apprentice Xehanort really had amnesia, then Xemnas really didn't know his heartless was running amok and/or didn't know his heartless was like Ansem. When we meet Xemnas in KH1, he only seems to remember Ansem The Wise.
Good point. Though it's heavily implied the Organization finally found out about Ansem during the final chapters of KH1, because by the time we get to Reverse Rebirth, Zexion, Lexeaus, and Vexen all seemed to have a decent idea of at least what he was and what he tried to do. I believe Zexion even mentioned him by name.
The only thing I can see really making sense of all of this is if Xigbar was there to influence Ansem and Xemnas' actions... which is logical. Braig would have been there when the split happened. If Apprentice Xehanort really had amnesia, then Xemnas really didn't know his heartless was running amok and/or didn't know his heartless was like Ansem. When we meet Xemnas in KH1, he only seems to remember Ansem The Wise. Anyway, Xigbar could have easily instructed Ansem about the princesses of heart as the key to opening "The Door To Darkness" and even set him up to be at Destiny Islands for Master Xehanort's 3D plan. It's also very easy to believe that Xigbar was influencing Xemnas early on. And of course, Xigbar's actions all go back to the MoM. Which would make Xehanort a little tragic, as his whole life was nothing more than manipulation after manipulation by the MoM... somewhat fitting as Xehanort manipulated so many others
Yeah, that sounds reasonable enough. I'll probably just accept this explanation for now, unless perhaps a better one presents itself.
Hm....maybe the reason Ansem knew about it all is because he was harboring Master Xehanort's heart, like how Xemnas harbored Terra's.
I bring this up because I remembered a line from Re:Coded's first secret ending, bringing up how Xehanort's heart was seized by his Heartless half.
Both MX and Terra's hearts were freed after AX did the ol' stabby stabby.
MX was in Ansem, and Terra was in Xemnas.
Both Ansem and Xemnas became independent beings eventually, but in the time it took for them to become independent, they still had MX and Terra influencing them.
That's actually a really good observation! Xehanort and Terra had a very similar disposition to that of Ventus and Sora, and we know that it's implied Ventus' dormant heart may have stayed within Sora's body/Nobody (explaining Roxas' appearance). Who's to say that when Apprentice Xehanort split himself apart, Terra's didn't stay in his Nobody the same way Ventus' did?
However, the one issue I see with this idea is that technically, Xemnas wouldn't really be a "Xehanort" in any sense, would he? He has Terra's body and soul, and was hypothetically influenced by Terra's heart. Does that kind of makeup constitute him being one of Xehanort's "selves" throughout time? Aw, but maybe we shouldn't open that can of worms.