One-handed katanas = fail.
Katanas are not Claymores.
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They can be dual wielded in real life like most swords, extremely difficultly I should add. Not impossible though. Not to mention be used with a shield if you are an expert.
Katanas are more like Bastard swords than anything else. Either one handed or two handed.
A light sword like most Katana can be used with one or two hands. Daedric should so be two handed.
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That said, arguments aside, the heavier the weapon the less likely it is able to be wielded in one hand.
Perhaps you're thinking of a Nodachi? Which is a very large two handed Katana class weapon.
Also, I'm not trying to make you angry, I'm just showing what I know.
Also, yeah, D-11 has it right. They should be used in two hands.
However, should, doesn't mean must.