mmd_tools is a blender addon for importing MMD (MikuMikuDance) model data (.pmd, .pmx), motion data (.vmd) and pose data (.vpd). Exporting model data (.pmx), motion data (.vmd) and pose data (.vpd) ...

The many free VMD motions which you can download from the internet almost always require that a model must have ... and which require turning off a character's leg/foot IK when applying the motion to ...