I tried converting PLC_NT_Myrkul_roid04 and PLC_NT_Myrkul_roid04_idle.GR2 into an FBX file using the drag-and-drop method, but the imported FBX model didn't have an armature. I think you mentioned earlier that the tool would add at least one bone, so I'm probably not understanding something.
The tool will only create bones if there are bones in the input files. You should also convert the file containing the skeleton, which in this case is PLC_NT_Myrkul_roid04.GR2, however, I tried it and the tool doesn't find any skeleton within the file. After investigating it, I found out that the file contains a skeleton but not exactly in the way the tool expects. I need to generalize the code for finding skeletons.