Kuja's motive was very cliche. He wanted to replace Garland as the ruler of Terra and Gaia, like he told the party, in Terra. The only thing that makes him diferent from other villains, is that he wanted to conquer TWO worlds, instead of just one.
Really going out of your way to lie these days, aren’t yoU Crystal?

I’ll use a tactic you know nothing about: EVIDENCE to disprove your weak assertions.

A cliche villain would be power-hungry for the sake of power hungry. He is EVILLLLLL and he does BAD THINGS because...he’s an evil, bad person.

That’s not Kuja.

Kuja: Oh, how I've longed for this day.
Kuja: ...the day I might finally cast away this mask to reveal my true self.

Kuja: The final act will take us away from Gaia, and I will kill my nemesis...with my own hand!

Kuja wants to kill Garland...because he’s just a cliche and evil?

Kuja: I must destroy him before Terra's plan is activated, or my soul will no longer be my own!

It was either destroy Garland or Terra’s Resurrection would carry out and the Genomes, vessels for the true people of Terra, would be done for and Kuja’s soul would go to whoever it originated from.

Garland: I constructed the Genomes to be vessels for the souls of the people of Terra when they awaken.

What does Garland say of Kuja’s motivation?

Garland: He is only hiding it. He denies his own identity.
Garland: He rejects the meaning of his existence and tries to assert his own individuality.

Kuja doesn’t want to be seen as a someone else’s creation: as merely a vessel for someone else. He wants to establish his own power, his own will.

Kuja: The weak lose their freedom to the strong.
Kuja: Such is the way of the strong. And it is the providence of nature that only the strong survive.
Kuja: That is why I needed strength

Bu Kuja’s own assertions, it is the “providence of nature” that the weaker beings are subjugated by the stronger. He flatly acknowledges Garland is stronger than him and so he seeks to overcome this. As Hilda said
“ He was a hopeless narcissist”

For someone with such a strong will and ego as well as a philosophy that the strong should be the rulers of all below them, Kuja’s longing for power was a way to justify himself and defy his “destiny.”

Afterall, look at what it is that drives Kuja over the edge.

Garland: There's a limit on your life... You'll be dead soon...
Even as I die, you'll have died without ever leaving your mark on the world...

Kuja will never have the chance he longed for: to reject his existence, the life and destiny of a disposable tool.

Now witness fate’s ultimately cruel irony on the twisted and warped psyche of Kuja’s mind:

Kuja: What comedy! Zidane, isn't it hilarious!? I'll die just like the black mages I so despise!
Kuja: I single-handedly brought chaos unto Gaia, but in the end, I'm nothing but a worthless doll!

Despite his lifelong ambition to attain power to signify his individuality, he would die before he eve rhad the chance to build his “eternal kingdom.” Thus, in the desperate last acts of a man trying to elude the claws of death

Kuja): ...I won't let it happen.
Kuja: I won't... I won't let this world exist without me!

Kuja: Why should the world exist without me? That wouldn't be fair. IfI die, we all die!

In the mind of a half-crazed egotist of the highest order, the destruction of all lesser beings is the only right thing. He, Kuja, is the best and most powerful of all of them. By what right should they live while he perishes?

Kuja’s character and ambitions are merely something many fictional characters wrestle with: Fate. Destiny. The idea that free will is an illusion. Kuja tried to prove himself as an individual by attaining power. He ultimately failed because he could nto escape his destiny.

His final acts, even in the throws of death and after killing Zidane and his crew is to save them all.

Perhaps it is in that act alone Kuja finally escaped his destiny: the destroyer of Gaia, the taker of lives for a master and being a slave. He was a slave all his life...to Garland and his own greed. But in the end, he saved lives.

Kuja is anything but a cliche.