Thoughts on this Tanto

[Rivkin]

The extra thickness might hint Tosa, but Tosa Yoshimitsu tends to long kaeri or in rare cases if I remember correctly yakitsume with kaen, this one has simply a very short, well formed kaeri. Tosa tends to have more subdued nioi-guchi. Tosa tends to be pure suguha based with very little variation, maybe a bit of notare - this one actually has well defined gunome-like elements.

 

I personally would investigate one of the schools known for non-distinct midare hamon and sometimes has short kaeri.

Fuyuhiro, for example. Then again yasurime is also quite distinctive.