Characters of the Final Fantasy XIII series - Wikipedia
Yeul is probably the weakest of the three but that makes sense given the mechanism she presents. .. We actually see Noel and Serah develop a relationship. . Noel and Caius are still my favorite hero / villain of the series. So do you think Yeul loved Caius? Caius Loved Yeul. "knight in shining armor," similar to Kimari and Auron's relationship with Yuna in FFX. I've just finished XIII-2 and I still cannot see Caius and Yeul as a couple at all. .. through doors is, of course, the most important part of a romantic relationship.
On Gran Pulse, Fang regains her memory and remembers it was she who became Ragnarok, a monster designed to bring down Cocoon  during a conflict between the two worlds called the War of Transgression. After the defeat of Orphan, she and Fang transform into Ragnarok and form a crystal pillar to prevent Cocoon colliding with Pulse.
After this event, Vanille remains with Fang in crystal stasis within the pillar: She is dubbed a saint and lives in the city of Luxerion in the protective care of the Order, a religious organization devoted to the deity Bhunivelze.
After their parents die years prior to the start of the game, Lightning, then still called Claire, raises Serah and sets out to become a protector for her, but her devotion to that goal causes tensions between them. Eventually, Serah becomes engaged to Snow days prior to the start of the game, and Lightning strongly objects to their relationship. Serah eventually reveals to Snow and Lightning that, while exploring the Pulse Vestage where the fal'Cie Anima was kept,  she has been made a Pulse l'Cie.
Serah reconciles with Lightning, who accepts her relationship with Snow afterwards. She is the only one who remembers Lightning being on Gran Pulse after she is taken to Valhalla, with all the others believing she sacrificed herself to save Cocoon. After Serah accepts Noel's offer to be brought to Lightning, the two embark on a journey across time to find her sister.
In the process, Serah encounters Caius Ballad, while learning from Paddra Nsu-Yeul that she possesses the same detrimental ability as her to see the future. Serah appears to Lightning in Valhalla as a spirit, telling her she knew that she could have died from her visions but still took the risk regardless.
Serah promises Lightning that they will see each other again as long as Lightning promises to remember her. Early in the development of XIII, Serah was meant to be a playable character, but was eventually delegated to a supporting character because of technical issues. After becoming a l'Cie and finding Serah in crystal stasis, he despairs and is forced to tame his Eidolon, the Shiva Sisters.
Once Hope gets Snow alone, he unsuccessfully tries to murder him for his part in his mother's death and reconciles with him soon after.
Snow then reconciles with Lightning and receives forgiveness from Hope's father. His search would eventually result with him traveling through time while seeing Lightning in a dream telling him to protect the crystal pillar holding Cocoon, seeing a vision of the world's fate, and becoming a l'Cie once more with the Focus of fighting beside Serah at the final battle.
Serah and Noel come to Snow's aid and help him defeat it by negating the anomaly causing its growth. With the threat gone, Snow entrusts Noel with Serah's care and dissolves from the moment in time while promising Serah that they will meet again. In Lightning Returns, after being released from his imprisonmentSnow meets up with Noel and Hope before coming upon the city of Yusnaan and becomes its protector and patron.
He was designed around a motif of ice,  with his bandanna inspired by an unused costume element from Kingdom Hearts coded designed by Kamikokuryo.Final Fantasy XIII-2 - Movie Version -4- Caius And Yeul
At the beginning of the game, Hope and his mother Nora, on vacation in the town of Bodhum, are selected for the Purge. Under Snow's leadership, Nora joins the resistance in the Hanging Edge, but falls to her death during the battle while trying to protect Hope and after saving Snow's life, which angers Hope greatly. After he becomes a l'Cie, and being separated from the main party, Hope follows Lightning to "toughen up" while plotting his assassination attempt on Snow for revenge.
When on Gran Pulse, he tells the others to leave him, afraid they will get hurt because of him, but inadvertently summons his Eidolon Alexander. After the defeat of Orphan, Hope tells Lightning that Fang and Vanille had changed their fate by fulfilling their Focus of transforming into Ragnarok to save Cocoon rather than destroying it.
He helps Noel and Serah in their journey to find Lightning when they arrive in his time.
Paddra Nsu-Yeul | Final Fantasy Wiki | FANDOM powered by Wikia
Other than knowing that time travel is possible and wishing to undo events of the past, Hope is planning on reviving Cocoon with a different power source. Originally planning to create an artificial fal'Cie, he is dissuaded upon seeing a vision of Serah fighting his creation.
When the old Cocoon does fall, Hope and Sazh manage to rescue Vanille and Fang from the crystal pillar before it crumbles. His son, Dajh, is taken by the Sanctum in the aftermath of him becoming a Cocoon l'Cie three days earlier when Sazh bought him a chocobo chick.
Caius rests her lifeless body in the Sea of Chaos along Valhalla's shore and she disperses into light. He sees Yeul's implanted vision of the crystallized Cocoon crashing into Gran Pulse and a glimpse of Etro's shrine, and summons an army of Rift Beasts to enact his war on Etro.
Caius faces off against Lightning. Caius challenges Etro's protector Lightning to battle. As she and Caius meet face-to-face he grabs her 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 as they continue their duel. Noel falls from the sky through Etro's gatethe portal to Valhalla, the goddess having answered his prayer to gain the power of chaos to follow Caius.
Lightning saves Noel as Caius pursues the two in the form of Chaos Bahamut and engages her in an aerial dogfight. Lightning defeats him, but he reappears and summons a meteor above the Temple of the Goddess. Assuming Lightning is dead and will not interfere, Caius uses his knowledge of foresight over the ages to create 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 and destroy the timeline.
As explained in Final Fantasy XIII-2 Ultimania Omega, even though Caius cannot time travel, once his preparations are complete the place and time of his plan will become so badly affected by the chaos he will be able to enter there from Valhalla. Caius contacts Alyssa in a dream and has her give a booby-trapped artefact to Noel and Serah. When the two use the artefact to open a Time Gate, they are separated in the Historia Crux and end up somewhere within the Void Beyondan unstable world of chaos that exists in-between the Time Gates.
Noel and Serah are ambushed by a future incarnation of Caius who first defeats Noel and places him in a dream world. Stating he is impressed by Serah's strength, Caius explains Etro's interference with the events of the Day of Ragnarok caused a time distortion that cut Yeul's lives short, along with his intent to kill Etro, before impaling Serah and sending her to a dream world of her own.
Serah and Noel escape their respective dream worlds and pursue Caius to Academia AF, the time of the prophecy when Caius plans to destroy both the old and new Cocoons so the countless extinguished lives would force Etro's gate wide open and let the chaos of Valhalla seep into the mortal realm. As Academia is infected with chaos Caius is able to arrive there from Valhalla.
Serah and Noel chase after Caius into the sky on an airship and defeat him as Chaos Bahamut. Caius returns to human form and admits he is impressed by Serah's determination to change the future even if it means her death due to being a seeress like Yeul.
Caius remarks Noel would have made a worthy Guardian, and says everything he ever did was 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. He transforms into Chaos Bahamut and flies into a wormhole that opens in the sky. Caius engages Noel in battle.
Noel and Serah follow Caius into the wormhole and emerge in Valhalla where Caius confronts them on the beach. Noel attempts to convince Caius that Yeul willed to be reborn to see him again, but Caius refuses to listen. He launches a ball of fire at Noel and Serah sending them falling into a bottomless abyss beneath Valhalla's waves of chaos. As Caius is about to kill Noel, Yeul intervenes saying the future has been changed.
She tells Serah and Noel that changing the future also changes the past, and Caius leads her away so Yeul would not see the future any further, taking her to the Augusta Tower to spend her final moments. Feeling she can trust Serah and Noel after learning they are trying to protect the timeline, she believes they could grant her wish for her future selves to not see Cocoon fall.
Yeul reveals secrets to Serah and Noel. When Serah and Noel arrive in the Augusta Tower from Academia AF, Yeul gives them an artefact and reveals Caius uses her visions to remember the entire timeline, and that he is immortal.
Yeul says Serah's sister Lightning disappeared from Gran Pulse because the future was changed, and if Serah and Noel continue to solve the paradoxes, the past will return to the way Serah remembers it.
She reveals the Caius the two encountered in Academia was a fake created by the tower's sentient AI, and that they saw the real Caius in the tower. Yeul tells Noel and Serah to show her a new future. After they venture into the core to defeat the AI, Yeul sees a vision of a future with everyone smiling, and dies happy, before Caius takes away her body. Yeul of AF Yeul dying in Noel's arms. If I were to live, it would bring contradiction to Inspired by the strength in Hope's eyes, Yeul aspired to be strong like him.
After foreseeing her own death during the Cie'th outbreak in Academia, Yeul ventures there. Noel holds Yeul in his arms as she explains her survival would have caused a contradiction to the timeline, and says Caius isn't in the city. She tells Noel she is not the Yeul he knows, but thanks him and dies, leaving an artefact for him and Serah to open a new Time Gate. Her death is negated in the alternate timeline set by the defeat of the Proto fal'Cie Adam. Yeul of AF Yeul promises Noel they will see each other again.
You don't have to cry. We will meet again.