From: CharCustomZaku | #483
That was really Jenova that said that and killed Aeris
No, it wasn't.
Well, sort of. Sephiroth was manipulating Jenova and accomplishing his will through her. Everything that the Sephiroth you see in Disc 1 did is exactly what the real Sephiroth wanted done.
I remember there used to be a debate about whether Jenova was controlling Sephiroth or Sephiroth was controlling Jenova. Then Square released the Ultimania that definitively stated that Sephiroth was controlling her the entire time.
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