.. my 0,02 EUR on that matter:
Ninjas
.. oh no, please don't do that. There wheren't any people like black-clad mummy clans which stalked the night.
Those where an "invention" of Hongkong filmmakers who hired some workers from the docks as "sword fodder".
There
where some stealthy assassines out there, but they didn't hide in the dark but under the disguise of common men
edited: or women 
. So if you're giving the nation an assasine, make it look like some peasant or something.
dual wielding
It isn't "barbaric" to wield 2 Katana, it's almost impossible. Even using Katana/Wakizashi at the same time is technically difficult, so it's a thing for elite troops only.
2-handed swords
The Katana is basically bastard sword, it can be wielded both 1- and 2-handed. In it's "final" form it's not longer than european Longswords.
However, it's just that the swords got shorter over time. The first Katana, and before them the tachi even more, where 20 to 50cm longer and 2-handed only.
[
barbaric swords
Using 2
straight swords was considered barbaric, simply as it was
chinese
But was only after ~900, the very first swords in Japan where imported chinese weapons, or derived from those, and had an straight blade.
There's that tale about that "swords of the gods" (cannot remember the name ..) that is described as straight and 2-edged, though.
Everything AFAIK and IMHO, o.c.
yours
Arralen
[ January 06, 2004, 05:13: Message edited by: Arralen ]