Mii

Miis are customizable characters that were debuted alongside the Wii via the Mii Channel, the Nintendo 3DS, the Wii U via the Mii Maker, the Mii Maker via Nintendo Switch, and on iOS and Android devices through the Miitomo app. Their name is obviously a reference to the name of the Wii and the fact that the character can reflect the player (and of course others as well). They've since become a phenomenon and arguably the mascot of the console excluding Mario.

Once the player has created a Mii, they're then allowed to place the character in a game of their choice and turn them into a playable character.

On the Nintendo DS, Miis are used in games like Personal Trainer: Walking and Tomodachi Collection.

The Miis live in a small pocket-dimension called Mii Plaza. A new version of the Mii Plaza is present on the Nintendo 3DS in the application titled StreetPass Mii Plaza, where they are the main characters of Puzzle Swap and Flower Town, and the main protagonists of Find Mii, Mii Force, and Monster Manor.