切腹 the formal word 'Seppuku' = cut+stomach/abdomen (or more popularly used in the West, 腹切り 'Harakiri' = stomach cutting) was traditionally performed by people of Bushi ranking/status with a good blade, in pristine condition.
Anyone carrying such a utility knife would not be permitted to perform seppuku with it, well, not formally, unless they were desperate for something, anything at hand... and then it would be called 自刃Jijin = die by your own blade/hand, not necessarily cutting the abdomen, but the throat etc.
For this reason, Greg, I do not think searches using the word 'seppuku' would be historically valid, as its primary purpose would surely not have been for seppuku.
Incidentally, there was plenty of crossover in weaponry between the Ainu, outcasts, and Karyudo/Matagi hunters, i.e. people outside regular Japanese society. It could even be such a hybrid piece.