Shun Narukami Knives are comprised of carbon steel clad in stainless steel.  This is intended to provide a "best of both worlds" scenario for premium cutlery.  Carbon steel blades have a tighter grain structure and get sharper than stainless steel.  It is also a tougher steel that is less prone to knicks or chips.  The downside is that they can rust without careful maintenance.  Having clad the blade with stainless, only the exposed edge needs to be watched.  As you use this knife, the exposed area will darken and turn grey creating a beautiful two-toned appearance. Referred to as a "patina", this is a form of oxidation that will help prevent red rust.  A patina will develop fairly quickly on a knife that is used regularly, often within a week or two.  In terms of performance nothing gets sharper, or is easier to resharpen, than carbon steel and Hitachi Blue Steel 2 is an excellent carbon steel.