Japanese Knife Blade

[sabertasche]

Hi all, I won this small blade on ebay thinking that it was a kozuka blade. It was labled as a "ninja knife". Despite the lable and poor photos, I put in a low bid and won the auction. What arrived in the mail is a bit of a mystery. The construction is quite facinating despite its' small size. I believe it is too thick to fit a kozuka handle and the blade too wide to fit in a saya. It appears to have a hamon or at least a hardened edge.

It looks Japanese but as to its purpose, I have no idea. I am Intrigued by the "rat tail" tang, it must fit on to some form of handle. Has anyone else seen a similar blade? I'm hoping a more learned collector can shed some light on my newest "ninja knife."

Regards,

Greg