A No-Dachi.
A really big Katana with and elongated handle. I'd have my hilt be a foot and a half long, and I'd hold it revered and behind me.
If not that then I'd use a short concealed blade that looked line a cane or something, or a set of knives with sharp wires attached, I'd throw the knives to fake people out and curve them to wrap the person up, then cut them to bits with one tug(Not sure if that even counts as a melee weapon).
A Kusarigama is also appealing(Google it)