When I checked the operation with Blender, nothing happened, but when I converted it to VRM with Unity, the legs and some skeletons of the 3D model are bent strangely.
There was a "root bone" at the position of the bone at the waist, so replacing the waist bone increased the number of legs from two to four. enter image description here
Since there was nothing in the operation check of Blender, I'm not sure if there is a problem on the Unity side or the problem on the Blender side.
Method After modeling, I will do the following methods.
Associate the VRoid skeleton with "the mesh with Automatic Weight". I am checking the movement of the bones in animation and pose mode.
"Weight transfer" takes place as the costume follows the body. One of the causes may be that the bones are interfering at that time.
When exporting, check the following items. ・Apply Scalings: FBX All
・Select Armature and Mesh
・Geometories：Apply Modifiers
・Amatures：Only Deform Bones
・Animation：Baked Animation