Freaky. I think they draw a couple images and use animation to fill in the rest
AI software. Similar to what's going on with the deepfakes.
This just looks like Live2D to me, same sort of thing as what all those VTubers use. This type of thing doesn't require anywhere near the complexity of deepfakes.
It's not magic, just tween and puppet. It's almost easy.
Show us how to do it!