Hey lopezar,
I myself have never really used this particular method but I have seen it done before.
Get a small piece of "fine course" sandpaper and start to lightly sand over the decals.If you press to hard, you will sand into the paint as well.
Also if you have any reference material on the Ki84, check to see how the a/c is weathered and see how the markings appear.
When you attempt this method, make sure you have a protectice coat over the decals(so nothing peels or moves on ya)
Flaps up, Mike
If you would listen to everybody about the inaccuracies, most of the kits on your shelf would not have been built Too Close For Guns, Switching To Finger