Battle of the 1000 Heartless

Battle of Hollow Bastion was a major event that took place in Hollow Bastion. It featured 1000+ Heartless attacking the Restoration Committee and their settlement. Organization XIII purposely began the war to collect more hearts for Kingdom Hearts. Maleficent also participated in the battle in an attempt to seize the world as hers again.

The Committee
The battle began while Sora and co. opened the DTD databank in Ansem's computer and were discussing Ansem's identity with the King. When the Bailey was destroyed by the surge of Heartless, the party immediately made their way there, but were forced to linger in the halls of the Castle fighting their way out.

Meanwhile, the Hollow Bastion Restoration Committee made their way toward the Bailey, and then to the Great Maw, to combat the threat. They made themselves ready as thousands upon thousands of Heartless flowed toward the town. Aerith made her first in-battle appearance in the series, aiding Yuffie with her white magic skills, revealing her to be able to cast the Cure spell herself. Cloud and Leon fought side-by-side against a large crowd of Heartless, both making comments regarding their former battle together on this world. Cloud has a short reunion with Sephiroth, then runs off after him just as Tifa arrives. Even Stitch, Yuna, Rikku, and Paine help in defeating the Heartless, although do not have as much of an effect on their numbers.

As Sora and the gang make their way down the Ravine toward the Great Maw, the Committee arrives in various places to help them get down, then disappear to continue the fight.

They do not appear again until after the fight, but it can be assumed that they spent most of the time fighting nearer the town, defending it from advancing Heartless. They appear to be mostly unscathed, and quickly begin working on repairing the town once more.

Sora & Co.
Although a small minority of Heartless were attacking Ansem the Wise's old castle, Sora and his friends forced them back out of the town into the Great Maw. Sora, Donald and Goofy caught up with King Mickey in the Bailey, and defy his orders, going in to help their friends. Upon reaching the Castle Gate, they encounter Demyx, who they previously met in the Underworld at Olympus Coliseum. After a tough battle, Demyx falls and fades back to darkness. Mickey catches up with Sora, Donald and Goofy, accepting to help them. However, a Surveillance Robot's laser hits a boulder which would have hit the King, if Goofy had not pushed him away. Goofy, being hit on the head instead, is seemingly dying or dead. Enraged, Mickey, Donald, and Sora charge into the battle. Sora is then helped by Yuffie, Leon, Tifa and Cloud to rid the Heartless. However, after the battle through the passageways, Sora, Donald and Mickey discover that Goofy is alive.

The group move into the Great Maw, where they finally beheld the leader of Organization XIII, Xemnas. Mickey runs off to confront Xemnas. Before the others can follow, they find themselves surrounded by a great Heartless army. Sora, Donald, and Goofy split up to finish off the numbers quicker, and a great battle ensues, leaving only the three warriors of light standing. The trio eventually catch up with Mickey. Xemnas makes his departure, chased by Mickey into a corridor of darkness. The three briefly have encounters with Axel, Saïx and Maleficent, the plot of the Organization revealed to them. Maleficent surprisingly saves the three from a group of Heartless and sends them away from the world, ending the war.

In Game
In-game, Sora must defeat exactly 1000 Heartless alone. The battle can be made much easier by using the Reaction Command, however. This allows Sora to perform Rising Sun Reaction Command, which lets him attack large groups of enemies and devastate them. The Armored Knights are relatively helpless in this way, and to make matters easier, Sora can grab the Surveillance Robots around the area and use them in the Snag Reaction Command to attack the Armored Knights and other Surveillance Robots. In the end, although the Armored Knights are not exceptionally strong, their main strength is their great numbers, which compounded with Sora being alone could catch him off-guard. These Heartless are in fact weaker then the normal variety found, possessing less HP and stats. Because of this large number of Armored Knights, the battle could take a long time to complete. But because of the Reaction Commands, this battle is very easy, albeit long.

The battle was made even easier in Kingdom Hearts II: Final Mix+, with the addition of Limit Form, which can be activated without any allies.

Commanders

 * Sora
 * King Mickey
 * Leon

Combatants

 * Donald
 * Goofy
 * Yuffie
 * Aerith
 * Cloud
 * Stitch
 * Tifa
 * Cid
 * Merlin
 * Yuna
 * Paine
 * Rikku
 * Tron
 * Claymores

Heartless Side

 * Maleficent (commander)
 * Pete
 * Thousands of Heartless

Organization XIII

 * Xemnas (commander)
 * Saïx
 * Demyx
 * Hundreds of Nobodies
 * Several Heartless (allied with Organization XIII later in the war)

No side

 * Sephiroth
 * Sark
 * MCP
 * The Hostile Program
 * Axel

K.I.A

 * 1000+ Heartless
 * Many Nobodies
 * Demyx
 * The Hostile Program

W.I.A.

 * Goofy (Knocked unconscious, thought dead)

Aftermath
In the aftermath of the battle, Maleficent's power over the Heartless was effectively broken. Organization XIII was able to take control of them, and began sending them to the worlds which Pete had previously visited.

Sora began to doubt his purpose, knowing that Organization XIII would take the hearts of any Heartless he would defeat. However, Goofy reminded him that to do nothing would allow the Heartless to continue taking over worlds.

Also, in the dark world where Maleficent sent the party after the battle, the trio obtain several critical clues that lead them eventually to Twilight Town, and then to The World that Never Was.

Trivia

 * In the cutscene prior to the battle, Sora, Donald and Goofy wield their basic weapons (Kingdom Key, Mage's Staff and Knight's Shield, respectively). However, when the fight starts, they carry their equipped weapon. This is because the cutscene was pre-rendered. This is probably because of the amount of objects that were in the area.
 * In the cutscene, black Behemoth Heartless are shown. However, Behemoths never appear in Kingdom Hearts II, except with the help of cheat codes.
 * Another battle featuring 1000 heartless can be found in the Underworld as match 45 in the Hades Paradox Cup. Like the Hollow Bastion one, it also features Armored Knights and Surveillance Robots.