Modder finds that Breath of the Wild uses "advanced" Mii file format for NPCs
Every day, there are fans out there discovering new and interesting facts about video games. One such person was a Twitter user named HEYimHeroic, who figured out a curious detail about how The Legend of Zelda: Breath of the Wild generates its NPCs. Apparently, the game uses a modified version of Nintendo's Mii format for its human characters, and through this and some "advanced" tweaking, you can inject your own custom Miis into Breath of the Wild. These files, called UMii's, use certain details from Mii characters, such as hair style, eye color, and facial hair, though not every detail gets transferred over. HEYimheroic reported that they'll be taking commissions to edit people's Miis into UMii files for use in modded versions of Breath of the Wild. with intent to share the method with the public once they understand more about the process.
So, do BotW NPCs use Miis? Both yes, and no.
Basically, they use an evolution of Miis, which the game's files call "UMii"s (which is what I'll be calling them from now on). UMiis have almost all the same parameters as Wii U/3DS Miis, with a few minor differences here and there, like moles no longer being supported.
However, BotW does not support every hairstyle Miis do. So, if you tried to load a hairstyle the game doesn't support, it instead calls a separate file, that essentially converts the unsupported hairstyle into a hair type that is supported and looks the most similar to the unsupported one, which is what happened with my personal Mii, Alice.
There's a lot more details I could go into, BUT I'd like to spread the word about this a bit more before other people start reposting my stuff, so I hope you don't mind. Thanks
Source