Jack Dover
Surprisingly this didn't occur to me, even though there were tempering issues with my other Japanese tools.

I thought that maybe this blade has to be broken in, since it wasn't used. There were other tools having a crumbly edge from hardening\tempering, but doing ok after some metal was ground off exposing a properly tempered part. I'm going to give it another attempt while correcting some issues and if it doesn't work - I'll try tempering. There's nothing to lose at this point, the blade is not operational anyway and it wasn't expensive at all. I have a small toaster oven graduated to 450F, shouldn't have problems producing 325-350F.