Parent bone & Child bone
Click the article to watch the video.
Click the article to watch the video.
Click the article to watch the video.
Click the article to watch the video.
If you have updated Robust Weight Transfer from old version (like v1.0), it might crash Blender.
MMD is fine for posing, but in Blender (and many other 3DCG softwares), you can use something called Rig (not to be confused with rigging).
If you want to manually trace motions, you should move body first, then limbs, hands and facials.
There are some AI tools that can auto trace videos, or even make motions from scratch.
FBX, glTF and more: