Quote Originally Posted by Andromeda View Post
That not I'm sure. He was praying to the planet or lifestream whatever, but I don't know she needed to be in the lifestream to manipulate it. Because she died though she did return to the lifestream, where everyone goes back to if I'm remembering things right. It is also the will of the planet or something, since the planet can actually take action by using the lifestream to heal or defend itself. The weapons are part of that defense system. So I sort of doubt Aerith was needed for anything. The planet was going to probably act in defense of itself anyway, which Sephiroth wanted. Well he planned to make enough damage to do so, but it gathering as a preventive measure or after the fact still worked in his favor.

Though Aerith being in the lifestream and Cetra probably is the reason she can still exist as a single consciousness and do all sorts of hand wavy things to help out Cloud.
I thought the planet and its healing and the lifestream were 2 seperate entities. The fact is shows aeris at the end just as the lifestream centers toward the action, it fades out on her face as if to tell us that it was her doing. I think she lured sephiroth to the city of the ancients using the white materia in order to summon holy and sacrifice herself for the good of the planet. This explains why she went by herself and claimed that 'only she could stop sephiroth'.

It should also be noted that REDXIII said that holy was "having the opposite effect"