I love ruining everybody's fun. j/k I actually find it more interesting to think about, when there's an error in writing logic you end up wanting to abridge it with sense and imagine what else must have factored in. What exactly would adjoin his heroic reputation, those scenes before the burning and with Genesis to his god complex? What is going through his mind while he's inside the planet and stringing along Cloud?
I would just love a remake with more focus on the surreal, insane, things that must be flowing through his unworldly mind. If he becomes more like a god, wouldn't that make him privy to a rather nihilistic impression of life, much like how a depressed person starts looking at everything like a bunch of toy blocks they're bored of playing with? After all his body is burnt.
Maybe his vengeance towards Cloud is his way of staying in touch with humanity, an emotionless passion he should have discarded.
That's more of a leap and more just something I'd like them to explore, the difference between people, who're trapped in cages barred by their human emotions and limitations in perception, and a god like Sephiroth who once took their shape.
Griffith in Berserk had something going on like that, except prior to the 'ascension' Sephiroth was more directly afflicted by Jenova cells that had their own motive. Genes come into it too, as well as altered consciousness.
Reunion is my favourite track in the game. It feels like a pro Sephiroth song, it's surreal, and yet it's somewhat 'devoid' of tone and of emotion even if it definitely is a pleasantly relaxing piece. It makes me think of how this all is from Sephiroth's enlightened and detached perception.
Still.
Before all that, he was a mad killer after being a loved hero.
It's probably the Jenova cells that made him act nuts.
Funny, he's been the best society has to offer and then the worst kind of person after, then a god. All because of forces out of his control. Perhaps he's a commentary on how life for some people is futile and they'll always be in the thrall of things beyond us, and then in trying to escape his predicament by taking control and being god, he actually accomplishes what Jenova might want.