This is the final destination for Ventus, so make sure to leave no unfinished business behind in other worlds and do some grinding in the twisters of Twister Trench in preparation for the final battle. There are four chests and one Sticker in the starting area, the Seat of War: a Mega-Potion directly behind Ventus, a Sticker, an Elixir, and Xehanort's Report 12 in a wide nook off the path, and a Map by the exit. Allow Ventus to get swallowed by some of the twisters in the next area, particularly if he still needs to work on maxing Commands in order to meld Second Chance, Once More, and Leaf Bracer. There are also plenty of chests in this area: Wind Raid and a Mega-Ether are by the rock formation in the center of the area, a Mega-Potion by the wall to the right, and a Megalixir by the wall to the left. Enter the next area for a save point and, once ready, continue forward for some boss fights.
After Aqua is knocked unconscious by Vanitas, Ventus stands up to face the boy embodying darkness for the first time on his own. While Vanitas' HP has increased since the last encounter with him, Ventus should also be far more prepared by this point. Make sure to have Ventus' strongest Keyblade equipped, which at this point should be the recently-acquired Lost Memory, in order to maximize the damage dealt by Ventus' Commands. The Commands collected across Ventus' journey should be sufficient in this battle, but if you'd prefer a decisive victory, the fast and hard-hitting Sonic Blade can be melded to counter against Vanitas' own speedy and hard-hitting offense. Some of Ventus' new Action Commands, such as Superglide and Counter Rush, should also come in handy against the powered-up Vanitas.
While Vanitas' movements haven't changed much and his attacks remain largely unchanged, he does have a few new tricks up his sleeve. When Vanitas burrows into the ground leaving only a smoky shadow behind, Dodge Roll continuously or use Glide to escape from the darkness. Failure to do so will result in getting hit with an uppercutting strike of Vanitas' Keyblade, or if Ventus isn't standing directly over the shadow, getting pelted by Fire balls that Vanitas drops all around him. Vanitas may also attempt to combo Ventus by first hopping onto a stream of Keyblades, which he steers in order to spear right through Ventus. Dodge Roll or use Shotlock to maintain invincibility while attacking, as the combo only continues from there; he lands with a pound of his Keyblade, forming an iceberg that shoots out of the ground and freezes Ventus if nearby, and follows up with a vertical crescent slash of his Keyblade that morphs into a projectile.
After the battle, Vanitas' face is finally revealed, as well as the source of the Unversed. Vanitas then merges with Ventus to begin the final battle inside Ven's heart.
Boss: Vanitas (χ-blade)
The final battle with Vanitas has come; Vanitas has entered Ven's heart, fusing with him and creating an incomplete version of the χ-blade. This tremendous weapon has not only increased the strength of his attacks and changed those he can use, but his HP has also increased a great deal. Ven has access to D-Links, Shotlocks, and Command Styles during this battle, so make full use of them.
Vanitas will first charge his weapon, surrounding it and himself in a damaging aura. The attack is indicated by the lines "Forge the χ-blade!", "What's yours is mine!", or "Show me anguish!" He will then proceed to lunge at Ven with the massive weapon, slam the ground and create an X-shaped shockwave, perform another lunging slash, and even shoot a homing blast of energy in the shape of an "X" at Ven. Dodge Roll can be used to avoid this attack. Note that if Vanitas is attacked while charging the χ-blade, the attack is cancelled, so Reversal Slash can be used to avoid damage altogether and cancel out the attack. The boss also still favors the dark lightning attack, and he still has the ability to vanish and appear behind Ven. However, rather than performing a single, downward strike, Vanitas will use an attack called Dark Splicer, similar to Time Splicer, wherein he will slash Ven multiple times while teleporting around him to attack from all sides. Dodge Roll until he stops or, a more preferable option, block his attack. This leaves the boss open to damage from Counter Rush.
Vanitas also may begin to utilize an attack called Dark Spiral, similar to Riku's Dark Aura, charging at Ven at a fast pace multiple times, while the χ-blade cloaks him in dark energy. Dodge Roll can be used to avoid this. The attack can be predicted by the quotes "There's no escape!", or "Darkness waits!" While Ven should continue to use a hit-and-run strategy, it is advised to use Tornado and Mine Square to interrupt Vanitas's combos while still dealing great damage to him. Physical attacks should not be used as the main offense, as this will open Ven to Vanitas's attacks. Instead, utilize magic or other long-ranged attacks to the fullest.
It is impossible to fully deplete Vanitas's HP once Ven deals an attack that should defeat him. Instead, Vanitas's HP will remain at 1, and he will then shatter the pillar on which he and Ven are fighting on. Vanitas will then become a temporary D-Link, granting Ven the attacks that are key to defeating him once and for all, which uses his own attacks against him. As the two Keyblade wielders float in a dark realm amidst shards of stained glass, Ven can move to Vanitas's location and hit him with Dark Spiral or Dark Splicer. However, it is recommended to merely use Ven's only available Shotlock, Dark Link. This will cause Vanitas to fire his own version of the attack, Dark Cannon, to counter. As the two beams of energy collide, rapidly tap a button or spin the analog stick to win the grapple. This method can also be done with the Dark Spiral and Dark Splicer attack. This must be repeated several times before the combo finisher, Last Word, can be activated. Once this is done, Ven will surround Vanitas with three beams of crystallized light. He will then shatter them, defeating Vanitas once and for all. However, Ven can miss when performing this attack, therefore timing is crucial.