Shade
Monster Junkie
I'm thinking it's a sword-version of a BFG, hence "BFS".
If we make it an exotic weapon with a higher reach it opens up a can of worm regarding PCs getting their hands on it, so I'd much rather make it something intrinsic to the creature. Either give it a "sword" attack that's actually a special weapon attack (or attacks) that's intrinsic to its body, have it possess an extended Reach, or simply make it a Huge creature so it has a natural 15 ft. reach.
My first vote's for Huge, and failing that, just give it longer natural reach.