When using the VMD plug-in with Koikatsu, the arms and wrists will twist in strange ways when using motions. After a while it will look like this. This will happen even with different motions and models. Is there a setting that needs to be adjusted or another plug-in that can fix it?
By using MikuMikuDance? You can't if i remember. Sorry
Go to "Anim", "Joint adjustment", make sure Right & Left forearms groups are disabled.