The Gathering

The Gathering is the name of the secret ending of Kingdom Hearts II. It is also commonly known as Sunset Horizons after the piece of backing soundtrack used during the video.

Summary
The video starts with the view of a desert. A semi-transparent Ansem's Report scrolls down the screen where one of them explains a detailed article on the Keyblade. There are a few shots of metal objects lying in the sand. The screen shows a man in armor, Terra standing amidst the desert waste, on the remains of a large construct decorated with various spikes. He looks to one side and sees another armored figure, Aqua approaching. Terra turns his head again and sees the third figure, Ven, also approaching. As Aqua and Ven come closer, Terra walks towards three Keyblades standing alone in the wasteland, as the thing he was standing on dissipates in the same fashion as a dead Nobody. The three keyblades are Kingdom Key, Way to the Dawn, and Kingdom Key D. Terra takes the Kingdom Key, Ven takes Way to the Dawn, and Aqua takes Kingdom Key D.

The screen zooms out to show Terra, Ven, and Aqua standing in the center of a field of keychain-less Keyblades, one of which resembles the Fenrir Keyblade. They stand still for a few moments before something catches their attention and they all look up. A figure, too blurry to make out in the heat, is walking towards the three Keyblade Masters and words appear, briefly, on the screen in this order: "Master of Keyblade", "The lost two, "Memory of Xehanort", "Chasers", "Keyblade War", "It all began with..." and the screen goes blank showing the last caption entitled: "Birth by sleep".

Speculative Meanings

 * Master of Keyblade: Possibly Master Xehanort or Terra, Aqua, and Ven's master's
 * The lost two: Possibly Master Xehanort and his apprentice.
 * Memory of Xehanort: Possibly the reason behind Xehanort's amnesia
 * Chasers: Possibly meaning Terra, Aqua, and Ven who are seeking Master Xehanort and his apprentice. Some fans speculate that "Chaser" is a rank given to one who can create a Keyblade, as in the real world, the word "chaser" refers to one who engraves metal.
 * Keyblade War: Possibly a war fought over the Keyblade, or between Keyblade wielders
 * Birth by Sleep: Name of upcoming game, also may have something to do with the infamous "Room of Sleep" Xemnas created and frequently visits, or with the Unversed. It could also refer to the granting of Keyblades to new Masters, since both Sora and Roxas Dove while asleep.
 * Also, in the Kingdom Hearts Final Mix secret video Deep Dive, there is a phrase that comes up that says "A world between = A forgotten world. The Gathering." This may have something to do with Sunset Horizons, the world. It could also have something to do with the upcoming game Birth By Sleep and the memories of Xehanort. However this is still unknown.
 * It may be possible, however, that the none of the words at the end of the video (Master of Keyblade, The lost two, Memory of Xehanort, Chasers, and Keyblade War) have happened yet. This is derived from the movie ending with it all starts with... Birth By Sleep.