The Nine Guardians of Light - Sora, Donald, Goofy, Riku, King Mickey, Kairi, Aqua, Ventus, and Lea - arrive at the Badlands outside the Keyblade Graveyard. They are confronted by none other than Master Xehanort himself, who explains the legend of the first Keyblade War, and how the universe they know was created when darkness overtook the worlds following the War. Master Xehanort wonders aloud if they will be found worthy of the light the legend spoke of. Ansem appears and suggests that they may just as well find all of creation will be destroyed, and that they are recreating the legend today to see. Xemnas arrives and opines that the Guardians' light shines too brightly and must be purged for good measure. Vanitas and Young Xehanort are the last of the core Seekers of Darkness to arrive; Vanitas declares that only when the Guardians's hopes have been broken by the Keyblade War will the key to Kingdom Hearts be created, and Young Xehanort affirms that this is what has been preordained all along.
The Seekers of Darkness disperse as a massive horde of thousands of Heartless, Nobodies, and Unversed arrive to do battle. The Guardians of Light disperse into groups to fight the insurmountable horde. Sora, Donald and Goofy combat their own portion of the horde, and despite throwing everything they have against their enemies, Donald and Goofy observe that they need to take them out in groups since they just keep coming. The fight escalates to the point that they summon the Big Magic Mountain Train, whose firepower is sufficient to whittle down and decimate the enemy horde.
The trio goes on ahead to where the others have gathered past the entrance of a cave, where Terra appears to have materialized to meet them. Ven excitedly goes to greet his long-lost friend, but Aqua, having seen more than her fair share of dark illusions, recognizes that it's not Terra and demands that Xehanort let him go. "Terra"'s hair turns white as he reveals himself to be Terra-Xehanort, the same incarnation of Xehanort who Aqua sacrificed herself for a decade ago. Terra-Xehanort declares that before the Guardians even face the Seekers of Darkness, they'll be stripped of their hearts. Though Sora refuses to be beaten by him, Terra-Xehanort swiftly cuts down Ven and Lea in short order. He moves to kill Kairi, and Sora is too distraught to do anything but use himself as a human shield to protect Kairi. Goofy manages to deflect the killing blow in time, and Donald musters every ounce of power at his disposal to cast the almighty Zettaflare spell, which sends Terra-Xehanort flying.
The price of the victory is steep, as Donald collapses from the exertion. Sora is in shock at how fast Terra-Xehanort brought down a third of their group, but Riku orders him to pull it together as Demon Towers begin spawning. However, their power grows too vast to counter as they form the gigantic Demon Storm, sending Aqua into catatonic shock seeing an old foe from the Realm of Darkness. The Storm quickly scoops up Mickey, Donald, Goofy, Aqua, Ven, Lea, and Kairi, leaving Sora screaming in despair. Riku tries to get him to get up, but Sora refuses, claiming he's worthless without all of his friends. Riku disagrees, and stands strong against the Demon Storm.
As the Storm begins lashing out to take Riku, the Keyblade Master draws his blade and counters it with all his strength as Sora watches in awe. However, Riku's last stand is still not enough, and he is consumed, and a tearful Sora is shortly thereafter.
- —"And so, as foretold, darkness prevailed, and light expired..."
In the past, Young Xehanort declares victory over Young Eraqus in their game, citing the legend of the Keyblade War to have come true. However, Eraqus is undeterred and pulls a surprise move, using light from the past to give himself a last-minute assist...