Caius Ballad is the antagonist of Final Fantasy XIII-2. He tries to stop Serah Farron and Noel Kreiss from changing the timeline, saying that they're the ones causing the anomalies with their time travel. However, his true motives are revealed as the story unfolds.
His goal is to free Yeul from the curse of death and rebirth, and also freeing himself of witnessing her dying over and over again. To accomplish this, he must destroy time itself by killing Etro and unleashing the Chaos of Valhalla over Gran Pulse.
Lightning Returns: Final Fantasy XIII
In Lightning Returns, Lightning encounters Caius once again, this time within the ruins of Etro's palace that now resides in the Wildlands of Nova Chrysalia. Caius manages to get a one-up on Lightning by hitting her with a curse that slowly drains her life as long as she remains inside the palace. However, she manages to make it to the throne room, where Caius awaits her arrival. The two fight, and Caius loses their battle.
Afterwards, Caius reveals that he cannot be killed, nor can he be saved. After he unleashed the Chaos upon Pulse, the many incarnations of Yeul that now reside in the Chaos took hold of him and refuse to let him free. Despite receiving what he sought in Etro's death and the destruction of the cycle of death and rebirth, he is effectively trapped in a net of his own making.
At the end of the game, after Bhunivelze's defeat, Caius and Yeul appear and proclaim that they will continue to reside in the Chaos and watch over the cycle of death and rebirth together, allowing humanity to thrive once more in a new world. Noel, however, protests, as he too wishes to be with Yeul. Caius, in an act of charity, allows Noel to move on to the next world with the last of the Yeuls; the only one that can be free of the burden that the other incarnations bear.
Of the main quest bosses, Caius is the only one that does not have a powered up form that can be encountered if the player waits until day seven to fight him.
Caius is voiced by Hiroshi Shirokuma in Japanese and Liam O'Brien in English.