Heart & Key

Heart & Key is the ending of Kingdom Hearts χ Back Cover. Like Blank Points, Signs of What's Next, and Another Guardian of Light, this cutscene utilizes in-game graphics and voice acting. It ends with the phrase "Reconnect. Kingdom Hearts," and it does not tease a future addition to the Kingdom Hearts series. Instead, it serves as a true ending and acts as a prologue to Kingdom Hearts III.

Synopsis
Unlike his fellow apprentices, Luxu does not receive a tome from the Book of Prophecies. Instead, he is given a mysterious box, and he inherits a Keyblade that contains his master's Gazing Eye. Luxu is told never to open the box he received, and he is instructed to journey afar with his new Keyblade. Following his master's orders, Luxu says, "May my heart be my guiding key."