Hi ryosuke, the folder you are talking about is the last framelock from the japanese Rockstead. That is a semi-custom factory, which in my opinion makes some of the best folders available on the market. They use two kinds of steel: one is a clad steel ZDP189+Ats34, the other is a DLC coated YXR7, a HSS tool steel. The main thing about these knives is the mirror like surface and the convex or semi-convex (Busse like) grind.
These knives are awesome, the price is that high for the quality of the materials used and for the craftmenship: they are made by an industrial process followed by a hand finish for the edge. These are the sharpest of my knives; I have two of them: the Higo and the Shin
Stefano from Italy