Heart of Chaos The Heart of Chaos is a manifestation of the goddess Etro , and it is her own heart . It resides within the chest of Caius Ballad . The " Heart of Etro " Caius possesses is Etro ' s " physical " heart , and not a kind of heart humans have that defines their person . Etro ' s heart uses different Japanese term than the " personality heart " . Etro ' s soul exists outside of it , but it ' s not specified where . The English localizations make no distinction between people ' s hearts and souls , but the two are separate entities in the Japanese version . Datalog . " The Heart of Chaos is the goddess Etro ' s own heart , given to Caius . It is the font of the immortal Guardian ' s power . Only if another potential Guardian defeats him and takes this power can Caius truly be killed . And the only person remaining in this world with that potential is Noel . " " If the new Guardian has enough strength of will , he can release the Heart ' s power and put an end to immortal destiny . If he wavers , however , he will be enslaved in chains of chaos , and become the latest in a line of eternal servants . " " The Heart of Chaos does not grant the Guardian power — it eats away at their physical self . Caius did not gain an immortal body , but was cursed with eternal life . " Fragment s . " Heed my words , Noel . You are the last protector , and the only one who can wrest the Heart ' s strength from Caius . In the instant you strike the life from his body , you shall either inherit the curse , or break its eternal grip . Only your will can slay fate one way or the other . " " A massive battle once raged on Gran Pulse . Paddra was besieged by a great army that sought the life of the seeress . In the face of this assault , Caius chose to perform an ' incarnate summoning . ' This ritual merged his essence with that of the Eidolon Bahamut , and drew forth all their latent power . " " An incarnate summoning expends the life force of the summoner , and thus Caius did perish . But he returned from death ' s domain , an immortal heart beating within his breast . That dark summons is now his to wield at will — as long as the Heart of Chaos pumps eternity through his veins . " " Etro granted the most selfless of gifts . Her power and strength flowed through the gate to the Unseen World , and with each passing second she grew weaker and weaker . " " Now the goddess sleeps within the Heart of Chaos . Should she cease to exist , then the power that she granted to humanity , the power that makes their universe whole , will disappear . When the sands of time run out on the goddess , so too do they on the world of man . " Story . During a time before the War of Transgression , Etro recognized the l ' Cie and Guardian Caius for dedication to protect the seeress Paddra Nsu - Yeul . In what she considered an act of mercy , Etro released Caius from his fate as a l ' Cie and " blessed " him with the Heart of Chaos so that he can protect Yeul ' s reincarnations throughout time . Etro ' s act , however , would be seen as a curse of eternity to Caius , as his body suffers pain despite being considered immortal , and he is doomed to watch hundreds of Yeuls die before his eyes . Driven mad , Caius waits centuries for the right person able to pierce the Heart of Chaos , therefore killing Etro and freeing him from his curse . The only person capable of freeing Caius is another would - be Guardian who can either destroy the heart or inherit it . Caius finds his pawn in Noel Kreiss in the year 700 AF and takes Noel under his wing and trains him to become a Guardian to Yeul like himself . When Noel shows the right potential , Caius challenges the unwilling boy to battle , hoping that Noel will release him . The duel ends with Caius ' s victory , and he resolves to kill Etro himself in Valhalla , the world dislodged from time where Etro is said to reside . Caius does not succeed as the goddess is protected by her champion , Lightning . As Noel and Lightning ' s sister Serah begin their journey through time to find Lightning , Caius creates a number of paradox es throughout the timeline . Caius places the two in danger from both his past self and the Proto fal ' Cie Adam . When Serah and Noel defeat Caius in Valhalla , he tries to provoke Noel into killing him . Although Noel refuses , Caius forces Noel ' s blade through the heart in what he calls an eternal paradox . This kills Etro as he had planned , causing Gran Pulse and Valhalla to merge into Nova Chrysalia as the chaos Etro had kept at bay is released . Caius had failed to realize he has doomed himself to another form of immortality , as he has been been bound to the chaos itself by Yeul ' s love for him — as revealed in " " , as long as Yeul doesn ' t want to let him go , Caius cannot disappear . If the Noel defeats Caius in Noel ' s dream world with Paradox Scope active , the paradox ending " Heir to Chaos " happens : Noel kills Caius and inherits the Heart of Chaos . Noel becomes immortal and he inherits Caius ' s memories , but states that he will not be like Caius , and will strive to save him , Yeul , and Serah . Musical themes . " Heart of Chaos " , composed by Naoshi Mizuta , plays during the final battle of Serah and Noel against Caius in Valhalla . It is a fast - paced arrangement of " Caius ' s Theme " .