"Huh. Explaining this is gonna be hard, dude." Xigbar scratched the back of his head for a moment, trying to compress it down in terms even Kaito could understand. "A keyblade is a special something. With a keyblade you can lock and unlock any lock, even the barriers between worlds. A keyblade can also collect hearts, which is how you make Kingdom Hearts. If you ask Tiger when we get back, I'm sure he'd show you his. "