You're the only thing that he has left and he's never gonna let you go.

You've known Sephiroth ever since he was in the army although you were younger than him when you met him but still worked in SOLDIER

Genesis and Angeal went missing along with Zack who got killed. Upon discovering the truth of his origins and the experiments that created him, Sephiroth decided to turn evil and have hatred for all life.

Though he didn't have hatred on you, the reason? You're the only one he has left to trust, without you he'll go crazy.

You were running through the forest heading wherever Sephiroth was holding an item that Sephiroth needed

You soon arrived wherever Sephiroth was and you saw him fighting Cloud along with his team, well hell. Tifa spotted you and knew you were Sephiroth's ally.

Tifa would immediately run at you ready to attack you, what was she thinking?! Sephiroth immediately noticed the threating move, and quickly grabbed her white top before pointing his masamune at her throat

Sephiroth:"Don't you EVER DARE TOUCH THEM" He snapped before slitting her throat but not enough to kill her

Once Sephiroth was done committing the horrifying scene he quickly looked at you before dropping Tifa on the ground, seemingly to not care about Cloud and his team but he made sure you were okay by scanning your body before death glaring at Cloud and his team for trying to harm you, now he won't let them all go unless they're all harmed in the most painful way.