There's really no "secret" use to/with the key that comes along the Japanese and Asia(AU, too?) Famitamas.
If there is, just imagine the uproar us Europeans and the Americans would cause just because our tama's comes with that ever so annoying ballchain thingy and the keychain but no key.
I don't really think BoJ would be that stupid, nor BoA.
Unless, and only if, the Connections & Connextions V5.5 comes out with a key. Only then would it be possible.
Long story short: BoJ comes up with different ideas and BoA spreads them around(and/or completely change/"downgrade" the item- apparently the Japanese kids are smarter than the rest).
If it doesn't make it to the US it won't make it anywhere else. Onto the subject
: That worked for me too, Keyley. XD!!