KH1: Ansem's Report 11

Opening the door to a world's heart causes its walls to crumble.

These fragments are seen as shooting stars.

This explains why these "gummi blocks" can travel freely to other worlds.

I know the catalyst of this collapse—the appearance of the Heartless. However, it will take time search out the worlds' doors and to retrieve each heart.

Furthermore, the doors can be locked using a Keyblade, making the heart forever unattainable. I must take action before the wielder of the key appears in this world.

If the princesses and the Keyblade are connected, they should resonate.

I've chosen a girl. I don't know if she holds the princesses' powers, but I will find out. She may lead me to the key bearer.

I shall set her free and observe.