X~Solar Boy Kal~X
Yes,but jenova could have fought sephiroth at any time,none the less died,but more so she didn't. i personaly think its the child/mother bond. iI mean jenova is a catastrophy from the heavens..don't remember what it really said. so none the less,she'd kil people. why not kill sephiroth? once again mother/child bond.
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Sephiroth had Jenova's cells in her before his birth, therefore making him apart of her. When Nibelhiem came around they worked together to get things done. Jenova was pretty much rendered immobile then and so needed a vessel to get things properly done. Seph freed her from the tank and went down into the Mako pit with her for their plans to begin.
Reunion starts. Clones waddle over to the Crater to Jenova.
Going over to the ending you can see themselves morphed into other forms due to the Jenova cells. They're still going about their Planet plan. Though, when her vessel's gone she left Seph to deal with Cloud alone in the crater.
In AC, Kadaj there merged with Jenova to bring about the true vessel needed. She, being the power giver here, couldn't carry it through all the way and there comes Kadaj back from seclusion.
Your point: I don't see much of a mother/child bond here. Why Jenova would fight with a piece of her I have no idea. Cloud was the one who went against her so he has a good reason to be attacked. I'm going back over to my virus theory here.