Sorry, Bailong, the katana is not solely a two-handed weapon. Almost all Iaido waza begin with a one-handed technique, then continue with a combination of one-handed and two-handed cuts, blocks, etc. Also, the power does not come from the hands the way you describe it. It comes from the entire body, and is directed through the sword by the movement of the arm/arms, allowing the blade to slice through its target.I'm not arguing that Duncan's use of the katana is authentic. This is a TV show, after all; the goal is entertainment, not authenticity. And I don't know how much the choreographers know about Iaido. At times, I agree, they display no real understanding of it. Other times, they do OK. But to criticize it based upon his using one-handed as well as two-handed strokes is simply not correct.   See 3 other replies

You can't blame the actor for his "mis-use" of the katana, that would be the lack of knowledge on the part of the fight choreoraphers. Still though a katana can be wielded with one hand, Musashi was known for that, and using daito and short sword at the same time is not unheard of. However, the choreographers do have him using it more like saber for film, lol. No suriage or kaeshi, lol. And I have no doubt they're tempted to follow the one handed approach because those blades are aluminum and light as hell.   See 3 other replies