Yep, Arthur and JD have the right idea; a small, single-shot dart firing device that would be built into the hilt of a shortsword or min-length longsword. The 'gun' portion would have to be integrated in such a way that it's all in the handle, or has padding over it (or both!)
Mario, those refrence pictures are nifty, but totally not safe to even attempt to build in a boffer.
I should add that I've been tossing around the idea of a secondary character in case something happens to Nara, and the Steamunk Fae from Constantius just sound like too much fun.
--Nara Darkstrider
Mercenary Guildmaster