This repository contains tools for the "MiiTube.dat" file that Miitopia uses in-game for character roles. The files are downloaded with SpotPass, it is nothing more than a package of a couple hundred Miis. Before you can play with them, they need to be decrypted. GodMode9 on a 3DS can help you out with that.
Usually on game startup it asks you questions about the Miis you see e.g. "Which Mii looks the bravest?" and rewards you with game tickets.
Being someone who works on RiiConnect24, I think the idea of Miis being distributed over SpotPass is neat, and it's the closest thing imaginable to what the Check Mii Out Channel was like.
This repository contains a Kaitai file structure of the format, and a bash script that can be ran to download the MiiTube files regularly. We download the files every 8 hours with a crontab on the RiiConnect24 VPS.
I agree it's a great name. Instead of "YouTube", it's all about me, so it's called "MiiTube"!