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Hmmm, I think it's just a result of someone having a large amount of darkness in their heart, but I don't know for sure. DarmaniSig 01:36, December 28, 2012 (UTC)

I believe it's explained as people with extremely strong hearts, becoming heartless...Although this makes no sense as to why Sora simply became a shadow heartless...At this point (due to Square-Enix's faulty explanation methods), I'm tempted to agree with Darmani, as it seems like it would be much more correct at this point.  Timelinesplitter Chaos 02:53, December 28, 2012 (UTC)