From Hello Kitty Online Wiki
As you progress through the main storyline, and wake each major NPC up, you will accumulate a number of "keys" in your key collection. Like the other collections, this is not an inventory, nor are these actual keys. Until you have a key, you cannot enter that NPCs above. Once you have a key, you can enter that NPCs abode at any point in the future.
Pages in category "Key Collection"
The following 17 pages are in this category, out of 17 total.