yeah, he uses Blender for animation with custom shaders while the models are converted from Koikatsu... (mostly the body and then headswap the character, there should be a plugin to do that)
his old animations used the body mesh by Shirakami, the most recent ones are based off some Koikatsu cards by AnnaAnon iirc
btw the Anis model was commissioned to a japanese guy called suyasuya who recently shared a PMX version of her:
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so I guess you could convert it to Blender with the MMD add-on
