As reported by engadget,
For years, fans have theorized that Nintendo used Miis to build many of the NPCs (non-player characters) in The Legend of Zelda: Breath of the Wild. Many share Mii-like characteristics — the shape of their face, eyes, nose and mouth, for instance — and modders know they were built with a file format called “UMii.” Now, though, we have even more proof of the cast’s design and origins. A Mii expert with the handle HEYimHeroic has discovered that it’s possible to convert and import traditional Miis — the ones that you can craft on the Wii, Wii U, 3DS and Switch — into the game.
HEYimHeroic has stressed that the Mii and UMii file formats aren’t identical. “The file formats are extremely different,” the modder explained on Twitter. “Which is why it takes me a while to import Miis into the game. There’s a lot of conversion going on, please don’t get the wrong idea.” There are some clear differences between the two. Breath of the Wild NPCs have slightly more detailed hairstyles, for instance, and full-size bodies. And while all of the game’s fictional races use the UMii format, HEYimHeroic explained, only the Hylian and Sheikah characters “use Mii-like values.” Even then, UMiis don’t support moles and select Mii hairstyles, the modder said in a series of posts on Reddit and Twitter.