It is a dramatic orchestral piece with a Latin chorus. "Caius's Theme" had a hard time getting approval from the director of Final Fantasy XIII-2, and Mizuta created more than four different tracks, spending nearly a month on this one track. The director wanted to make the song into something that could surpass Sephiroth's theme "One-Winged Angel" from Final Fantasy VII.
"Caius's Theme" is the leitmotif for main antagonist Caius Ballad. It represents his godlike status, as well as his grief and the tragic side to him. It first plays at Oerba -200 AF- during his confrontation with Noel Kreiss and Serah Farron, and during his fight with Serah at the Void Beyond.
"Caius's Theme" is a prominent motif and has several arrangements: "Chaotic Guardian" plays during Caius's appearance at Academia -400 AF- and during his battle with Noel in the Dying World -700 AF-; "Heart of Chaos" plays during the last battle against Caius in Valhalla; and the final boss theme, "Unseen Abyss", plays during the final battle.
"Caius's Theme" is the sixteenth track of the second disc of the Final Fantasy XIII-2: Original Soundtrack; "Chaotic Guardian" and "Heart of Chaos" are the thirteenth track of the soundtrack's third and fourth discs, respectively; and "Unseen Abyss" is the fifteenth track of the soundtrack's fourth disc.
"Caius's Theme" is also included in "Promise to the Future", "Endless Paradox", and the "Closing Credits".
"Caius's Theme" plays when he appears to Lightning in the Temple of the Goddess in the Wildlands. The theme is incorporated into the final boss theme, "Almighty Bhunivelze", and the ending theme, "Credits ~Light Eternal~". "Chaotic Guardian" is used during Lightning's battle against him, with "Heart of Chaos" replacing it after he is staggered at low HP. "Unseen Abyss" will play once Ereshkigal is staggered at low HP. Finally, a variation of his theme is used in "The Doomed Soul -Caius and Yeul-" during the cutscene following the battle.