Umabari/Bashin/Kankyūtō.
Sadly in poor condition, but it does have some redeeming features.
Fairly slim, the kasane at the Nakago ranges from 22mm~25mm. Overall length 22.1 cm, or nearly 8 3/4”.
The cross-cuts on the tang may have been to enhance thumb grip.
The characters for ‘protection against lightning’ (Kaminari yoké) 雷除 can still be seen faintly among the blade scratches. This was a general invocation against natural calamities like fire, flood and earthquakes, and the centers for such prayers were Kitano Tenmangu in Kyoto, Kaminari Jinja, etc.
Although used as fleams for horses’ ankles, there is a theory that they were pushed into the temples of trophy heads after battle for Kubi jikken before your leader.
And
雷除