Miitopia is a place where all of the Miis live, or whatever it is.
Miis were once intergalactic aliens from space, and in the year 1345, they visited one of Kittehlandia's moons to gather some rocks. But then Chuck Norris roundhoused the Mothership (Thinking that they were deadly, the Miis were actually friendly), and then the Miis crashed-landed onto the Kittehlandian analogue of Australia. The Miis were nearly extinct, so they acted fast and used up a ton of resources to keep their species going. Soon, they formed a culture there, and got stuck in time by keeping their world with medieval stuff. Nintendo decided to take over the land and decided to make a ton of shames about the Miis.