Yeah, I honestly wish that the FF7 movie was about Sephiroth being "cured" by finding out the truth, rather than about Cloud being cured from something he didn't even have in the game... or at least have them both be cured of their Jenova cells, perhaps at the same time.
Your fanfic sounds interesting. I remember when I beat FF7 for the second time, I thought it was strange that there was no alternate ending. Because the second time I beat it I had a more thorough playthrough. So I, and therefore Cloud and the team, learned the truth about who Sepheroth's mother was and why he turned out the way he did. Yet surprisingly, they never give you the option to try and talk to Sephiroth at the end about the truth, which almost seems cold hearted for the "heroes" to not do.
He has one of the most tragic stories I've ever seen. But for the want of his true mother's name, things could've been so different. He was lied to his entire life, and then his mind was taken over my an eldritch abomination that he thought was his mother. I don't understand how people still see him as the true "villain" of that story when there are so many factors involved. I'm over 120k words into this fanfic and hoping to be finished before summer's end, then to the edting