I'd imagine back stab's supposed to be done 2 handed to make sure the blade sink in deep enough to cause enough irritation and pain in the back. Other than that i'd look stupid and awkward to wield a small blade in two hands, merchant much?
Crossbows can be used one handed in real life, but won't be so accurate. Reloading is not possible if you seriously won't use other hand, unless you're shooting your will power!
In RO, pistols come in pairs!

It won't shot if you lost the other one!!

And it'll always shot 1 bullet from 2 pistols that might hit TWICE!!!

WHY IS THAT POSSIBLE?!!!
I think I'm finally going "home", renewal is fun, but there is really nothing like "heRO"...
Kyarorain, Shield Crusader
Erizabeth, Battle Sage
Derpette, Int Brewer
Katerine, Battle Acolyte