I often use blender_mmd_tools, but I will report a bug found in 2.91. When exporting an MMD model with the exporter of blender_mmd_tools (0.7.1, December 8, 2020 version) in blender 2.91, screen fraud ...
The Blender BVH importer has a bug. If you try to import a BVH file which has Japanese bone names, it won't import into Blender, and you will get an error message ...