Theres a few old videos (without sound) that im guessing are meant to be Mitsuki. She basically looked like a black haired version of the Mesugaki that RIM MMD uses. In fact if you check his latest work, it has a black haired version of her so you can see what that would look like.
I jusy went back into the Blendy thread to find the Mega link i remember being there which included those old files, and it seems it is the same model that Flim discarded. I've included the quote below, but it looks like the mega link was nuked.
You can check Flims Fantia and the old videos are available there for free (just need to create an account and follow him using the free plan). Just go to his earliest videos and the ones with the black haired twintails girl is, i believe, younger, flatter Mitsuki. I would normally link it myself, but (other than being a bit worried given the nuked mega above) i used to use Pixeldrain to upload and share things, but since they are apparantly starting to be against porn now I dont wanna risk that account given the already existing collection of videos i shared before in this thread as well as some others. Apologies. I believe they should also be available on Kemono or Nekohouse as well, if you dont want to create any accounts.