Appearance and Personality
He is a tall, slender, and muscular man with long purple hair and purple eyes. He wears a thin, purple bandana, grayish violet light armor, and carries a curve sword. He has a calm personality, and yet, as his plan comes to fruition, shows more emotion, such as rage grief.
Born prior to the War of Transgression, Caius is a member of the Farseers, the oldest tribe on Gran Pulse. The Farseers were led by a seeress Paddra Nsu-Yeul, who was gifted with the Eyes of Etro and thus able to see changes in the timeline and make prophecies of the future. Caius was made a l'Cie after killing Yeul's previous Guardian, after which he assumed the role. One day, Caius dueled with a formidable fellow warrior of the Farseers. Overwhelmed by his opponent's strength and skill, Caius was driven back until an enemy army invaded Paddra looking for the seeress, interrupting the duel before the final blow could be dealt. In Yeul's defense, Caius's opponent sacrificed himself to protect her.
Believing he should have been the one to die, Caius honored the fallen warrior by taking on his last name, 'Ballad'. To protect Yeul himself, Caius performed an incarnate summon to destroy the enemy forces, a skill that let him become one with his Eidolon but would cost him his life. Etro was moved by Caius's dedication and freed Caius from his fate as a l'Cie and infused her heart, the Heart of Chaos, into his body, making him immortal so he could protect every incarnation of Yeul until the end of time. Although given as an act of benevolence, Caius would eventually see his eternal life as a curse due to the madness he would have to endure.
The city of Paddra was destroyed in a civil war that broke out due to the seeress's prophecy of its fall, and Yeul cast away her role as the leader of Paddra. Her followers became nomads, and Caius was always by her side as her eternal Guardian. Whenever a Yeul would die a new one would be born and replace the old one. Though essentially the same, Caius saw each incarnation of Yeul for her uniqueness as he committed every one of Yeul's prophecies to memory while forced to witness her death countless times. Caius is slowly driven mad and longs for both himself and Yeul to be released from the cycle.
Final Fantasy XIII-2
Starting in 3 AF, Caius watches over Noel and Serah's progress alongside different incarnations of Yeul. Noel and Serah are time travelers who seek a way to Valhalla to reunite with Serah's sister Lightning, and prevent a bleak future, but every change in the timeline they make causes Yeul to witness the changes, shortening her lifespan. As a seeress she is forbidden from influencing the timeline to save herself, and Caius, as her Guardian, follows suit.
In 200 AF, Caius reveals himself to Noel and Serah during their visit to Oerba. Noel mistakes Caius for the one he once knew in 700 AF, although this is still in Caius's future. As Yeul had told him of Serah and Noel's actions across time, believing them to have been the cause of the temporal anomalies that threaten the timeline, Caius states his intention to punish them, but before he can deal the final blow Yeul intervenes, saying time has already been changed. Caius tells her they should leave to not see the future any further, opening a portal for the two of them to depart through.
Caius takes Yeul to the Augusta Tower upon her request, and allows her to meet with Noel and Serah in private and reveal his nature as her immortal Guardian. Yeul gives them an artefact that opens a Time Gate to the Proto fal'Cie Adam, and tells Serah and Noel they have the power to restore the timeline. Noel and Serah set out to change the future, and the subsequent change in the timeline causes Yeul to have another vision, which kills her. Caius laments on how her life was short, and carries away her body.
Two-hundred years later in the city of Academia, Noel and Serah are surrounded by countless Cie'th and are approached by Caius, who claims they were killed in the Augusta Tower after having learned of the "forbidden history", and because they stand before him alive and well, he accuses the two of being paradoxes. Noel finds Caius's behavior to be unlike him, and Noel and Serah pursue Caius throughout the city, learning from a Yeul who perishes after an attack from Zenobia that the Caius they were chasing was not the real Caius, and that he was never in the city.
By 700 AF, Caius is among the last remaining humans in the world and Noel is born in the Farseer tribe. Seeing that Noel is the one with the potential to free him from his curse, Caius takes the boy under his wing to serve as Yeul's protector. If everything goes according to Caius's plan, Noel will destroy the Heart of Chaos inside of him and kill Etro. Without the goddess, the chaos of the Unseen World will break free and flow into the physical world, ceasing the flow of time and freeing Yeul.
Upon learning Noel had defeated a Behemoth Caius acknowledges he is ready to become the one true Guardian, and tells Noel he must kill him just as Caius had once killed his predecessor. Refusing to succeed him that way, Noel tells Caius about his plan of going on a journey with Yeul to find other people so she will not be lonely anymore, but Caius says it is a futile dream.
After revealing his death and Etro's demise are the only way Yeul can be saved Noel's continued refusal to kill him drives Caius to force Noel to the point where he has to fight. Defeating Noel, Caius sees the boy is not strong enough kill him as he is now. Caius leaves for Valhalla after telling Noel that Yeul's feelings over his actions mean nothing to him, as his only goal is that she will be free upon Etro's death. With the Heart of Chaos, Caius finds his way to the Unseen Realm of Valhalla where Etro resides, this being the first time he abandons Yeul as her Guardian.
From Valhalla, a realm without time or death, Caius sees every era and every possibility in the timeline. While he cannot time travel, he sends messages to his past self from the Unseen Realm. Using the knowledge of foresight he has obtained over the centuries Caius creates a series of paradoxes to shape the timeline and create the right circumstances to execute his plan to force Etro's Gate to open so the chaos of Valhalla can enter Gran Pulse. As elaborated in Final Fantasy XIII-2 Ultimania Omega, Caius is aware his creating paradoxes across the timeline shortens Yeul's life, but his plan is to destroy the world in a way that minimizes the adverse effects his time-changing has on her.
As explained in Final Fantasy XIII-2 Ultimania Omega, when Serah and Noel solve the paradoxes the possibilities of the future broaden, but Caius proceeds to cut them down. As Caius's desire is to reduce the number of possibilities for the future to the point where only the world's inevitable destruction remains, he allows Serah and Noel to solve the paradoxes, because the world is still heading to its doom. Caius knows the world will end in 700 AF anyway, and wants to ease Yeul's suffering by destroying the world sooner than it is meant to happen.
While Caius's plans across the timeline are unraveling, he is simultaneously trying to kill Etro as she sleeps in her shrine. The goddess is being protected by Lightning, a warrior who was brought to Valhalla by waves of chaos and became Etro's champion. Unknown to both, the battle they wage in Valhalla is an endless loop, continuing for an eternity.
Back in the Dying World Yeul dies in Noel's arms and passes on to Valhalla. Noel believes he is the last human in the world, and prays to Etro to give him the power of chaos to follow Caius to Valhalla. Caius lays Yeul's lifeless body to rest in the waters off Valhalla's shore and she disperses into light. A saddened Caius asks if she never asked for this kind of eternity. He sees Yeul's implanted vision of the crystallized Cocoon crashing into Gran Pulse and Etro's shrine.
Caius summons a swarm of Pantopoda and other Rift Beasts to challenge Lightning to a battle. Caius's army is countered by her summoned army of monsters and Eidolons. As Lightning and Caius meet face-to-face, he grabs Lightning's gunblade and aims it at his Heart of Chaos which begins to glow. When Lightning backs away in shock, Caius transforms into Chaos Bahamut and sends Lightning flying over Valhalla. Lightning remounts Odin and she and Caius continue their duel. Noel falls from the sky of Valhalla through Etro's Gate, the goddess having answered his prayer.
Lightning saves Noel and Caius emerges as Chaos Bahamut and continues to engage her in an aerial dogfight over Valhalla and summons a meteor above Etro's shrine. Lightning asks Noel to bring her sister, Serah, to Valhalla, and sends him through a Time Gate to New Bodhum in 3 AF, where Noel and Serah will begin their quest to find Lightning and save the future as travelers through time.
Learning of Lightning's gambit, Caius takes advantage of Alyssa Zaidelle, whose extended life is a paradox, in Academia 4XX AF. Caius has Alyssa give a booby-trapped artefact to Noel and Serah, and when the two use the artefact to open a Time Gate they get separated in the Historia Crux and end up somewhere within the Void Beyond. Caius pursues Noel first, stabbing him in the back to release Noel's chaos before placing him in a dream world where Noel relives his past. Caius creates an illusion of Yeul to talk to Serah before personally engaging her in battle.
Caius admits he is impressed by Serah's strength and reveals how Etro's interference with the events of the Day of Ragnarok caused a time distortion that cut Yeul's life short. Caius impales Serah releasing her chaos as she enters her dream world. Believing himself free from the time travelers' interference, Caius continues his battle against Lightning in Valhalla.
Catching her off guard after she sees a vision of Serah dying, Caius strikes Lightning down and she is swallowed by chaos. Yeul's spirit summons Caius to fight Lightning in both his human and Chaos Bahamut forms, but Lightning emerges victorious. Caius goes to Academia 500 AF to enact a mass genocide of the new Cocoon's populace to force Etro's Gate to open. Final Fantasy XIII-2 Ultimania Omega scenario interview with Toriyama and Watanabe reveals that Academia 500 AF was so badly affected by chaos that Caius was able to enter there from Valhalla.
Serah and Noel escape their respective dream worlds and pursue Caius to Academia 500 AF where they catch up to him atop an airship piloted by Sazh Katzroy. Caius is impressed by Serah's determination to change the future despite not surviving to see it due to being a seeress like Yeul. Caius remarks Noel would have made a worthy Guardian and says everything he ever did, he did for Yeul. Believing the Yeuls being born only to die young is meaningless and cruel, Caius reaffirms he will stop at nothing to free them even if reality itself must be destroyed to achieve it. Caius transforms into Chaos Bahamut and flies into a wormhole that opens in the sky.
Noel and Serah follow Caius into the wormhole and emerge in Valhalla where the battle continues on the beach. Noel attempts to convince Caius Yeul continued to be reborn out of her own will to see him again, but Caius refuses to listen. Caius uses the chaos of Valhalla to transform into Jet Bahamut that launches a ball of fire at Noel and Serah sending them falling into a bottomless abyss beneath Valhalla's waves of chaos. The two are saved by Lightning, who sends them to the battlefield where the two defeat Jet Bahamut, along with his supporters, Garnet Bahamut and Amber Bahamut.
Having lost the final battle, a weakened Caius returns to his human form. He tells Noel that if it is his fault Yeul keeps being reborn, he must be killed for her sake. When Noel refuses, Caius attempts to provoke him by claiming he had killed Lightning. He says that since time does not flow in Valhalla as it should, the "things that shall happen" in their future have "already been decided" in his past, and he knows how their encounter will end. Caius provokes Noel by attacking Serah. Noel disarms Caius and lunges at him with his sword. Though Noel stops himself from killing Caius at the last second, Caius forces Noel's blade through his chest, destroying the Heart of Chaos (Given to Caius by Etro when he first showcased his dedication to protecting Yubel). The energy within the heart explodes and Caius fades away.
As revealed in the secret ending, "The Goddess is Dead", a revived Caius sits on Etro's throne in the Void Beyond. Though the Heart of Chaos was destroyed, hinted in the Final Fantasy XIII-2 Ultimania scenario interview, Caius has obtained a new form of immortality as he became one with the chaos itself since the many incarnations of Yeul desired his continued existence. From Etro's throne, Caius watched Noel and Serah's journey, stating they have been playing to his goal from the beginning as even their actions on alternate timelines had all converged and concluded with one moment: Etro's death. Telling Yeul they are free of their respective curses and can begin anew in a world without Etro, Caius releases the chaos to commence the end of time.
Lightning Returns: Final Fantasy XIII
After Etro's death, the balance between the Mortal and Unseen Worlds was destroyed, and the Chaos of Valhalla bled into Gran Pulse merging the two realms into a new world known as Nova Chrysalia, where people no longer age and cannot have children. For the next 500 years, Caius resides in what remains of Etro's Temple in the Wildlands from which the Chaos has been flowing. Though his only company is the various incarnations of Yeul, Caius still suffers due to his new existence as a personification of the Chaos he unleashed upon the world.
When Lightning visits the temple, Caius appears before her and calls her a mere "hunter of souls", and strikes her with his power. Lightning pursues him through the ruins and is assisted by the many incarnations of Yeul who wish for Caius to be freed from his suffering. Once defeated by Lightning, Caius stabs himself and shows her he is beyond salvation. He explains that Yeul had bound him to the dying world, a husk housing Chaos, as her incarnations are not of one mind: some desiring his prolonged suffering to end while others wish him to remain by their side. When Lightning asks him if he intends to sacrifice himself as atonement for bringing about the end of the world, Caius demands her to leave and disappears.
During Nova Chrysalia's final moments after Bhunivelze's defeat, Caius appears to Lightning and her friends alongside the many incarnations of Yeul he had protected throughout the centuries. Caius says there still needs to be a god to protect and save the dead in Etro's place, and the Yeuls declare their intent to become the new Etro to maintain the new world. As Noel protests the Yeuls' decision, Caius grabs him by the throat. He asks if Noel wishes to take their place in the Unseen Realm, and when Noel complies, Caius lets the last incarnation of Yeul leave with Noel to the new world while he remains with the other Yeuls to be consumed in Nova Chrysalia's destruction.