Here's an another off-the-wall idea: it's a rochin, from the Matayoshi tradition of kobudo. I just saw this a few days ago, and thanks for bringing this thread up where I could make the connection.
Check out this
YouTube video , and look at the weapon nearest the teacher's right knee. It's a long-handled, short-bladed, dao-like weapon about the length of the man's forearm, and the back is wavy. Matayoshi reportedly learned the weapon in China. For those interested, the "dao" rochin is discussed around 4:15 into the video.
Just a thought,
F