While Miitomo is not quite out yet in App Stores outside of Japan, Nintendo has opened up app access to Nintendo Accounts in the United States, Australia, France and other non-Japanese locations, while it prepares for launch.
Which means that if you have that app from the Japan App Store like I did, you can get a head start on a Mii attached to your Nintendo Account (or start a new one).
You can import your Mii from your Wii or Nintendo 3DS via QR code. From there, you can pile on pretty robust character customisation features, including voice (with straight to a T pronunciation for your name/nickname), behaviour and clothing, which is pretty non-gendered a la Animal Crossing. Early bird Miis get a Mario Cap.
You get coins as daily rewards, doing specific tasks, and answering questions your Mii asks. It’s definitely better when you get the friends on board. So get the app once it’s out!