>>11339507
It's been a very long time since I used sizebox, but last time I did IIRC all you had to do was put a .pmx (MMD's model format) file into unity with a plugin downloaded, press a button, and you got a sizebox-ready model. It was trivial although a bit annoying to download all of unity just for the sake of playing around with this loli foxgirl. But assuming they haven't changed it in like 8 years (big assumption) you just need to find some MMD models you like, download Unity and you're good to go.