An active and cheerful thief, Zidane exhibits fondness for women and is easily elated. But he has a strong sense of justice beneath that cheerful exterior, and cannot help but aid those in need.
A thief with great energy and a sharp wit, though all is lost when it comes to women.—Dissidia Final Fantasy description
Zidane is a thief who with the Tantalus Theater Group. Their mission is to kidnap Princess Garnet. However, their plans go awry, and soon Zidane’s caught in an international war.
On World B, Zidane, like Cecil, is fully away he has a brother: Kuja. They seem to be on friendly terms with each other too. So then around this time, Zidane would be aware of much more. When he starts the game, he only remembers a blue light. Now, he realizes that the blue light was of Terra, his home planet. He should also realize he’s a genome. However, none of this gets him down. He’s as carefree and cheerful as in most of Final Fantasy IX.
So when did Cosmo call Zidane to World B? It probably was not until after Pandemonium. While a machine tried depleting his soul, he falls into despair. He believes that his only purpose is for destruction. However, he snaps out of it. This is after Garland tells Zidane Kuja is his brother, but before they reconcile.
Garland: “You judge only by appearances. I mean someone with a soul similar to yours. The one I sent to Gaia might also be called your brother…And his name is Kuja.
Zidane: “Kuja!? He’s a Genome!? Impossible! He doesn’t even have a tail…”

The likely scenario is at the Iifa Tree. Here, Kuja lay wounded, left to die. However, Zidane goes back to save him:
Zidane: “Hey! Are you alright?”
Kuja: “Zidane…? What are you doing here? I thought I told you to go…”
Zidane: “Wouldn’t you do the same for me if you knew I was dying?”
Kuja: “…..”
Zidane: “……Never mind.”
Kuja: “Your comrades were able to escape?”
Zidane: “Yeah… I knew you had something to do with it.”
Kuja: “…I’m glad they made it.”
Zidane: “Yeah, well…it’s our turn to get movin’.”
Kuja: “………I don’t deserve to live after all that I’ve done. I’m useless to this world.”
Zidane: “No one’s useless…You helped us escape, remember?”
Kuja: “……After you guys beat me, I had nothing left…nothing more to lose. Then, I finally realized what it means to live…I guess I was too late.”
[Kuja’s head tilts to one side; he remains motionless]
But it’s unlikely that Kuja dies here. It seems that they would have spent time with each other during the year Zidane was away. During this year, perhaps the two brothers make it to World B.