Mii Studio (nintendo.com)

Accessed at https://studio.mii.nintendo.com, Mii Studio is a web app for any Nintendo account user to edit their associated Miis.

Implementation

Through "reverse engineering" (lol) we have found out this information about Mii Studio:

Storage Format

Miis are stored in Mii Studio using the browser's local storage. They are encoded in base64.

Here is a Kaitai Struct definition:

Mii Studio Local Storage.ksy

Rendering

Mii Studio appears to render Mii data through layering. It uses WebGL to draw onto a canvas, and then does a series of draw calls with transformations.