One-handed katanas = fail.
Katanas are not Claymores.
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.
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.