Enacting plots of utter cruelty while maintaining a graceful demeanor have caused many to fear this young man as the Angel of Death.
A sadistic, narcissistic silver-haired man of a delicate, epicene beauty.—Dissidia Final Fantasy description
Kuja is Final Fantasy IX’s effeminate, yet powerful, sorcerer and arm’s dealer. Only, he deals Black Mages. Throughout the game, he manipulates Brahne to help him with his own agenda: to summon Eidolons. And throughout Final Fantasy IX, he remains snarky, vain and narcissistic.
So then, at what point does he become helpful? During the twelfth cycle, Kuja remains on good terms with Zidane and the other Warriors of Light. He even assists him during their quests:
Kuja: “Zidane. Cheery as always, I see.”
Zidane: “Kuja? Why’re you here?”
Kuja: “Like you, I was summoned to this world as well. A poor pawn fated to battle.”
Zidane: “You too, huh?”
Kuja: “Seems we’re bound to each other yet. Unfortunately…”
Zidane: “Hey, have you gone to see Cosmos yet?”
Kuja: “I’ve visited her…as I awoke sooner than you.”
Zidane: “I see… Guess we just need to do our thing then. But I gotta tell ya, I never thought I’d get dragged into a battle of the gods. We’re in a different world and the others are in the same boat as us. There’s even an idiot who pulled on my tail since he’s never seen one! But I guess there’s no helping it, huh? Let’s end this quickly and head on home. So, we gotta face Chaos, was it? We just gotta beat his cronies, right?”
Kuja: “We don’t have the time to deal with them. Our enemy is the god of discord, Chaos himself.”
Zidane: “Chaos? You mean Chaos the god? But he’s got plenty of warriors, right?”
Kuja: “It’s pointless to face them head-on. Chaos can quickly heal their wounds.”
Zidane: “You mean it’s pointless to fight?”
Kuja: “Correct. That’s why we must defeat Chaos himself. His warriors will disappear if he falls.”
Zidane: “Disappear? That means…”
Kuja: “Yes, you are the same. It’s over if Cosmos were to fall.”
Zidane: “What the… Then we gotta get a move on!”
Kuja: “Yes, we need to start our preparations. I’ll look for a path leading to Chaos–“
Zidane: “Wait a second, Kuja. Isn’t it dangerous to go alone?”
Kuja: “I don’t like working in a group. And others would get in the way.”
Zidane: “I see…”
Kuja: “You should gather comrades you can trust. I’ll contact you again once I find a safe route. Bid my regards–to the others.”
There’s very little deception here. Kuja attempts to help Zidane and his friends. He only feigns deception to save himself. However, it’s to no avail. Kefka implants false memories into Kuja’s brain, of who the later revert to his callous self.

But why the shift in character? Kuja finds redemption at the Iifa Tree, doesn’t he? He appears to hold a grudge against Zidane during the 13th cycle; during the 12th cycle becoming friends with his brother. Did he survive the Iifa Tree?