Before I start I'd like to note that I have zero experience with modeling, blender, but watching a few videos and playing around with the options I was able to get it working.
A better method is probably out there, so follow these instructions knowing that.

1. Download Hakka's fan-made model.
https://bowlroll.net/file/306498

2. Watch this video and install all the requirement (seriously don't skip it if you've never used Blender, you won't understand the instructions if you don't)
https://www.youtube.com/watch?v=XbzAwwSWQts

*NOTE: You don't need to apply the "Fix MMD Model" option for this fan-made model, but DO apply the "Combine Same Materials" option.

3. If you watched the video you'll notice that the fan-made model has a lot of materials instead of the 5 or so in the demo, you'll have to enable VRM MToon Material for every single material, note down the texture name in the "MMD Texture" tab before you enable VRM, since that texture is the one you need to select in the "lit Color, Alpha" and for the "Normal Map" texture (two options below lit color) add the texture with the same name as the "lit Color", but that ends in _toon (Ex: lit color texture name: "_17.png", Normal Map texture name: "_17_toon.png") if it doesn't have a _toon texture you don't have to select one for the Normal Map.

*NOTE: The material called "00_Face_頬染め.002" is strange, I had to select the same texture as "00_Face.002" or I'd get a black face, feel free to tinker with transparencies and alphas, but that's the only way I found to fix it.

4. Watch this video to enable custom models in Desktop Mate.
https://www.youtube.com/watch?v=CqjfT6QzRLM

5. Enjoy your Hakka model in Desktop Mate!