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The box contains thirteen locks — three on its left side, three on its right side, and seven on the front with the lock in the middle being slightly larger. The crest on the box lid has thirteen spikes on the outside and seven on the inside. The red sigil of the emblem contains letters which read "χsuper" in it.
Kingdom Hearts χ Back Cover
Luxu later passes through the Keyblade Graveyard, lugging the box behind him.
Kingdom Hearts 0.2 Birth by Sleep -A fragmentary passage-
Kingdom Hearts III
Maleficent travels to various worlds along with her subordinate, Pete, searching for the black box, which, according to her, contains the Book of Prophecies. Luxord, a member of the real Organization XIII, has been tasked to find it, but he admits that he does not know what the box looks like or its contents. This leaves Sora confused on why the Organization would be searching for it. Luxord comments before leaving that the box contains "hope", further mystifying Sora.
Maleficent eventually determines that the black box does not currently exist, which is why she cannot find it anywhere, and that it will only appear after the second Keyblade War. After Master Xehanort's final defeat, Luxu stands in the Keyblade Graveyard with the box as the foretellers arrive while Maleficent and Pete watch from a distance.