Shin (our smith Kanemasa-Ono) has been busy forging the first Matsukaze blade. It was forged from a billet of Shirogami 3 (Also known as Shiro-ko), a steel with 0.8% Carbon. White steel (also known as “white paper steel”, named for the wrapping used by its manufacturer) is used to make tools that can be sharpened to an excellent edge with good quality natural stones. It is a carbon steel with only very small amounts of the impurities P (phosphorus) and S (sulfur). It has a very narrow range of temperatures for hardening (Yakiire and quenching), and thus requires the blacksmith to be very skilled.
The construction of the blade is, like the majority of historic blades*, in Kobuse around a mild steel core (Shingane).
* It is a misunderstanding that most of Nihonto have actually been constructed "Sanmai" or "Hon-Sanmai".