Obtaining all of the Graviton Cores and speaking with Alyssa will open up the next main story area, The Void Beyond in ???AF. You’ll be restricted to a linear path for a moment upon entering the area, so follow it until you can move freely again. Now go into the menu and configure your Paradigms. Serah and Noel are about to be separated, so you’ll need to make sure that each can survive without the other with the help of a monster. Make sure that you are prepared for a variety of different situations by configuring numerous different Paradigms. A few recommended Paradigms are: Slash and Burn, with a Ravager and a Commando; Lifeguard, with a Medic and a Sentinel; Undermine, with a Saboteur and a Ravager; Misdirection, with a Commando and a Sentinel; War and Peace, with a Medic and a Commando. Experiment with other options to suit your individual needs.
In order to compensate for the lack of a partner in this area, the wild monsters are a bit weaker than you are probably used to. Seek out Yeul. She is present in five different incarnations in this area, each of which will be marked by a waypoint. Finding her shouldn’t prove too difficult. Just be sure to stay on your toes and don’t let your guard down; these enemies may be weak, but you are not used to battling without Noel.
Each time you speak with Yeul, you will receive a Fragment and 600 experience points. A chest containing Live Trigger Rewards will appear after talking to the second incarnation of Yeul. The final Yeul is found up the steps in the Throne of the Goddess area. Performing a Moogle Hunt at the top of the stairs will reveal a hidden Chocolina, who you can buy some items from. Her inventory will be the same as it was last time you found her, however. Level up before speaking to Yeul for the fifth time to trigger a boss battle.
Boss Battle: Caius Ballad
Caius will immediately attack Serah each time you begin this encounter. After launching the initial blows, he will back off for a bit and buff himself for the upcoming onslaught. He will occasionally alternate buffing himself with debuffing Serah, so watch out for any status effect-inducing spells he may throw your way. Use the Lifeguard Paradigm as soon as the battle begins to ensure that you can withstand his attacks and counter his debuffs. After Caius begins to buff himself, you should switch to Undermine to counter some of those effects. For the remainder of the battle, alternate between the War and Peace and Undermine Paradigms, attacking Caius as he attacks you before switching to debuff him as he enters the stage of buffing himself again.
If you’re having a lot of trouble here, you can use Wounding abilities. These will gradually chip away at Caius’ maximum health, meaning that the battle will be a pure war of attrition. As long as you can survive long enough to reduce Caius’ maximum health to nearly nothing, you can win. This is not the recommended method of taking this boss down, but in a pinch it’ll do.
After fending Caius off, Serah will be spirited away from The Void Beyond and back to New Bodhum.