Japanese razors are a bit harder than western razors. So told me they go to 67 HRc in extreme cases.
More commonly they are 62-64, which is about the same as high quality customs. I know Tim Zowada come 63 HRC (or was it 62?) +- 0.5.
So asks a lot of questions indeed. Buying from So is slightly more complex than asking the price and handing over the money

I bought the nagura stone with mine, and I am very happy with it.
If I may ask, what are the dimensions?