Awataguchi Yoshimitsu is one of the finest smiths to have ever lived, and is mostly thought to be the best tanto maker of all time.
I was doing some research lately and found a blade that had more info than I could really understand with my basic Japanese. I talked to Markus Sesko about it and he uncovered a lot of interesting information.
It ended up that this was the blade used by the famous tea master Sen no Rikyo to commit seppuku. Have a read about it on Markus’ blog.