Game:Xion

Xion is fought as a boss in Kingdom Hearts 358/2 Days and Kingdom Hearts III. In Kingdom Hearts 358/2 Days she is fought multiple times throughout the game before finally serving as the penultimate boss. In Kingdom Hearts III, she and Saïx team up with each other at the Keyblade Graveyard to fight Sora, Kairi, and Lea. Her data also appears as a boss in Kingdom Hearts III Re Mind.

Kingdom Hearts 358/2 Days
In Mission 75, Roxas is sent to Twilight Town. Xion has left the Organization and is mistaken for the Organization impostor, Riku. Roxas has to track her down and "eliminate" her. Roxas attacks the imposter, but is stunned to realize he is fighting Xion.

She attacks Roxas in Mission 92, which takes place throughout various locations in worlds visited during the events of the game. Using the Organization XIII Devices, Xion is able to absorb Sora's memories from each world in order to replicate his abilities, and to some extent other elements of those worlds. For example, in Halloween Town, Xion uses Sora's Ragnarok and uses a weapon resembling the Chimera arm or The Experiment's arm, while in Agrabah, she uses his Ars Arcanum and has arms and swords resembling Kurt Zisa. Strike Raid is the only one of Sora's Kingdom Hearts special abilities that Xion does not use. Interestingly, the first three areas that Xion warps Roxas to are the locations of that worlds' respective Keyholes. In the case of Twilight Town, the Station Plaza is where Sora opens the world Gate.

Design
During Roxas's battle with Xion, she dons armor which changes a number of times throughout the fight. Her basic form is a bizarrely-shaped, predominantly silver and black suit, with dull red armor near her waist, gold on her boots, and orange armored gloves. Xion's helmet sports two black spikes that jut out horizontally on either side, and a large, red Nobody symbol on the faceplate, part of which forms something of a horn on the top of the helmet. This form is based on Sora's original appearance, with Sora's jacket, pants, and necklace, although Xion's pants are pink and have designs, and her necklace features a Nobody symbol instead of a crown.

In her first form, Xion sports large, skeletal, colorful wings and a huge, orange and red, intricately-shaped sword. In her second form, Xion loses her wings and grows to twice the size of Roxas, exchanging her sword for a large, pincer-like weapon vaguely resembling one of the Chimera's arms. In her third form, Xion transforms into a figure with four huge arms, decorated with elegant gold, purple and red designs. She has large blades instead of hands, and her arms resemble Kurt Zisa's arms. Her main body is slightly larger than normal in this form.

In her final transformation, Xion grows to a titanic size, about the same height as the Train Station tower in Twilight Town. Her armor is now embroidered with numerous spikes and ribbons, and she gains two pink and silver, Keyblade-like weapons with teeth in the shape of the Nobody symbol. Interestingly, this form has a similar design to Sora's appearance in Kingdom Hearts II, now being mainly black and dark grey.

Mission 75
Roxas may get stuck fighting the many Heartless in this mission during the search for Xion. Moving further into the Tram Common, Roxas sees Xion on top of a building, and she runs away. Xion does not attack, but only runs and dodge rolls, and teleports to another place in the area after taking several hits. The system for when this mission ends is unclear, as the timing for Xion to go to the secluded area is set at random. At the end of the mission, Xion teleports herself to the secluded place, where she waits for Roxas. Once Roxas reaches Xion, the mission ends, following a few cutscenes.

Mission 92
Be prepared for a multi-stage boss battle. During the fight, Xion transports Roxas to four different locations, each time assuming a different form.

Xion's attacks require good timing and careful maneuvering to avoid. Make good use of Dodge Roll and Glide. Equip Cure magic and/or Potions. Attack magic is effective but not essential.

First Form
The first battle with Xion takes place in the Bizarre Room of Wonderland.

Second Form
The second battle takes place in Halloween Town, at the Manor Ruins.

Third Form
Xion's third battle takes place in the Lamp Chamber area of Agrabah. In this form, Xion is more graceful and agile, performing flips and spins that make her difficult to hit. Xion's third form is difficult to dodge due to limited dodging room combined with Xion's agility and long reach. Land combos immediately after she stops attacking, and move away before she resumes.

Final Form
The final battle with Xion takes place in front of the Train Station in Twilight Town. She becomes massive, but remains stationary at one end of the battlefield throughout the fight. In this form, Xion loses both Counter Slash and Barrier, and her regular attacks are slow and telegraphed. However, her attacks can inflict status effects.

Kingdom Hearts III
Xion is fought at the Keyblade Graveyard alongside Saïx. Sora has Kairi and Lea as allies. Throughout the fight, Xion alternates between wielding her Replica Kingdom Key and copying Saïx's berserk state.

Xion's battle skills have effectively increased due to her possessing a fragment of Xehanort's heart. Xion will often teleport occasionally to where Sora or Kairi are standing. Once she reaches her target, she'll use multiple Keyblade thrusts to send the player flying into the air, ending her combo with her slamming them down with her Replica Claymore. She'll also occasionally enter a berserk state like Saïx's but the attack can be blocked by locking onto her. The fight automatically ends once enough damage is done to Xion and Saïx.

Kingdom Hearts III Re Mind
Xion's data is a secret boss in Kingdom Hearts III Re Mind. Her battle is significantly made harder.

Xion retains a few attacks from her battle at the Keyblade Graveyard, such as Strike Raid, her basic combo, and her rushing combo. However, she now has more attacks at her disposal. Like Roxas, Xion often teleports in streaks of light and summons light beams to attack. Her blue light beams, if they hit Sora, can temporarily cut down his maximum health down to 1 HP. She also has golden light beams, which do not have the same effect; she often telegraphs this by saying, "Let it rain!" Occasionally, she will shroud herself a yellow aura, signified by her saying, "Now you'll see!" or "Time to end this!" and her health being replaced with armor. From there, she enters a berserk state, where she furiously begins leaping around the arena and slams her Keyblade down at Sora. After three slams, Xion is vulnerable for punishment.

For her ultimate attack, Xion teleports outside the arena's boundaries and bathes the arena in golden light. She starts implementing more yellow beams while retaining her berserk state. This berserk state ends after a few minutes, or if Xion's armor is broken.

Unlike the other data battles, Xion is particularly hard due to her relentless nature. Understanding her patterns is even more crucial than in past battles to defeat her.

Trivia

 * During the battle against Xion: First Form, Roxas has been shrunk down despite not drinking the potion, and grows back to normal size when he is transported to the next stage without drinking the potion. Xion also changes sizes in the same way without explanation.
 * "Vector to the Heavens", the music that plays during Xion's final form, is a mix of Kairi's Theme, Musique pour la tristesse de Xion, and Dearly Beloved.
 * During Mission Mode, while battling Xion, she will not speak, due to some of her battle quotes being about Roxas.