The katana is nothing more than a sharpened metal bar and by no means compares to European sword design. There I said it.
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The katana is a great sword. Until you add armor into the mix. It's biggest strength is its slashing power, which you do not want to do against armor. European chain mail is good enough to stop an average swing and plate armor will always stop a slash, 100% of the time. And it doesn't have enough weight to do much blunt damage