Depths of Darkness

Kingdom Hearts 0.2 Birth by Sleep -A fragmentary passage-
Mickey Mouse and Aqua arrive at the Depths of Darkness where they come to the conclusion that Kingdom Key D can be found here because Sora obtained its counterpart before the islands were consumed. They fight off Demon Tide, and obtain the Keyblade. However, Aqua is dragged back to the islands by Demon Tide and blocked from joining the King.