Twitter user HEYimHeroic has discovered that the NPCs in The Legend Of Zelda: Breath Of The Wild are in fact based on the UMii format. They use an advanced version of the Mii format from the Wii U and the 3DS, with some parameter changes.
You can copy the Mii data into the game and make custom NPCs based on your Mii characters. Because the game does not support every hairstyle, it is transformed into a similar hairstyle that is available.
The Legend of Zelda: Breath of the Wild is an action-adventure game developed and published by Nintendo. It was released for the Nintendo Switch and Wii U on March 3, 2017. Breath of the Wild is part of the Legend of Zelda franchise and is set at the end of the Zelda timeline. The player controls Link, who awakens from a hundred-year slumber to defeat Calamity Ganon and save the kingdom of Hyrule.