A Fragmentary Passage

Zero point, also referred to as the Secret Episode (シークレットエピソード), is a secret ending exclusive to Kingdom Hearts Birth by Sleep Final Mix. Unlike other secret endings, Zero point is playable, much like the Final Episode, rather than simply watching from the view of a bystander.

In Zero point, Aqua is playable, the main setting being the Realm of Darkness, where Aqua fights several Pureblood Heartless while wielding Eraqus's Keyblade.

Synopsis
The secret ending opens with Sora sleeping on the Destiny Islands, with Kairi approaching him to wake up, mirroring the opening to Kingdom Hearts.

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Aqua is seen walking up to the cloaked Ansem the Wise, as seen in Blank Points.

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Clips from Blank Points are then shown rewinding, including the scenes between Braig and Xehanort and Terra and Master Xehanort and Aqua in the Realm of Darkness.

Zero Point

Aqua is then seen walking on through the Realm of Darkness, but stops when the realm starts to shake. A portal of light appears above her, and a ray of Darkness appears flowing directly into the portal. She clutches her Wayfinder to her chest.

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Aqua is then transported to the world Castle of Dreams, which has been engulfed in darkness. She looks in horror at the castle ahead of her.

A fragmentary passage

Mickey Mouse is then seen walking through the Realm of Darkness with the Star Seeker Keyblade, Riku is seen atop of Neverland's clock tower with Kairi in his arms, Donald Duck and Goofy are seen wandering through Traverse Town, Kairi, in her Kingdom Hearts II outfit, is seen with the Twilight Town Gang looking at the Old Mansion, and DiZ is seen in front of a sleeping Sora recording data, and Roxas and Xion are seen in Twilight Town with a blindfolded Riku looking down on them. Finally, a young Master Xehanort is seen on the Destiny Islands beach, then turning into Ansem, Seeker of Darkness, then Xemnas, then a flurry of clips showing the elder Master Xehanort. Sora is then seen sitting on the paopu tree in Destiny Islands, but disappears. Ventus is then seen in Chamber of Waking, but also disappears, leaving the room empty.

Birth by Sleep -Volume Two-