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Plot details for the Kingdom Hearts series follow.

In battle on Birth By Sleep, yes, he did. His Lingering Will finished him off. But it was more miraculous than based on factual strength between the two, it's a miracle Aqua was able to defeat Xehanort in Terra's body.  Timelinesplitter Chaos 13:02, December 21, 2012 (UTC)

So he was too old to fight or was Terra that strong? As for him losing to the Armor and Aqua, it might be something like not being used to the new body (like Captain Ginyu in DBZ) AkaAxl 13:43, December 21, 2012 (UTC)

Oh, you mean before the fight with the Xehanort in Terra's Body? Okay, yeah, that was because of Xehanort's old age, that's the secondary reason for him taking Terra's body, his primary reason being to live long enough to see his plan come to fruition. But yeah, Xehanort lost against Terra because of Xehanort's age.  Timelinesplitter Chaos 22:25, December 21, 2012 (UTC)