The Legend of Zelda: Breath of the Wild appears to use a modified version of the Mii character creator for its NPCs, and clever modders have even found a way to insert their own Mii files into Hyrule.

　　Eurogamer reports that dataminer HEYimHeroic discovered the files, which are referred to as "UMii"s in the Breath of the Wild code. The UMiis use facial components from the classic Mii designs, albeit with a greater level of detail and some stylistic touches to make them match the Breath of the Wild art style. UMiis do lack some features from their Wii/3DS counterparts, like moles and certain hair designs.

　　The discovery quickly led to the realization that modders can inject their own custom Mii designs into Breath of the Wild. That goes for many human and Hylian characters, but not the more distinct and less humanoid races like Gorons.

　　Hi, Mii expert here. Turns out, the NPCs in TLoZ:BotW use an advanced version of the Mii format. This means that with modding, you can inject Miis into the game. :)

　　Thinking about opening commissions for Mii injects, both screenshot/images of your Mii and mod downloads! pic.twitter.com/8NfVr4zyqA

　　— i'm alice (@HEYimHeroic) January 4, 2021

　　Main characters are bespoke designs that can't be replaced via UMii editing. Still, it's a neat way to inject some fresh faces into the Nintendo Switch classic, if you want your customized NPC to have a brush with the legendary hero.