The Black Box is a mysterious item referenced in Kingdom Hearts χ Back Cover and Kingdom Hearts III.
Design
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.
Story
Kingdom Hearts χ Back Cover
Luxu is tasked by the Master of Masters to keep the contents of the Black Box a secret from the other apprentices and deliver it to an undisclosed location.
Luxu later passes through the Keyblade Graveyard, lugging the Box behind him.
Kingdom Hearts III
Maleficent travels to various worlds along with her subordinate, Pete, searching for the black box. The box is mentioned again in The Carribean world when Luxord, a member of the real Organization XIII reveals his duty to find it. Though he admits that he does not know what the box actually looks like, he does infer that the box contains "hope". This leaves Sora confused on why the Organization would be searching for it.
After the defeat of Xehanort, the box appears alongside Luxu in the Keyblade Graveyard.
