For me I really don't think any Japanese natural will remove or erase the polish or refinement left by a Naniwa 12K and definitely not the edge left by an SG 20K, I just see the Japanese natural laying down its own edge, replacing the already higher level of polish and refinement that was left by the Naniwa 12K or 20k, in fact, I think I would use the Japanese natural directly after a 1K bevel set I don't see the point in using a 12K or 20K if you are going to replace that edge with natural stone, I think it defeats the object.