I cut down the arm blades and added a sword (fashioned from a gundam mock army heat cutter along with some plasticard).
As you can see, this isn't actually totally done: I need to go in and line-highlight many of the details.
Nevertheless, I was too excited not to share:
P.S. the ronin's sparring partner is NECA's otachi figure; which is absolutely fantastic (so much articulation!) and, in my opinion, absolutely worth the $60 price tag.