Sujihiki translates as "flesh slicer", which describes its role well. Typically 240 mm to 300 mm long and 34 mm to 40 mm high, the sujihiki blade is perfect for making long cutting movements from heel to toe. A lower blade height decreases friction when cutting and keeps the fibers of the protein you are cutting as intact as possible.
Simply explained, Aogami #2 developed by Hitachi Metals is a steel made from Shirogami #2 in which some chromium and tungsten are added for better durability and corrosion resistance. In addition to that, the higher carbon content of the steel allows for better cutting retention. Objectively, the Aogami #2 is an improvement over the Shirogami #2. For patina lovers, however, Shirogami steel will be more reactive to oxidation and could be an advantage.
Futana is the name of a line of Hitohira's house knives. As with all products that carry Hitohira's trademark (ひとひら (一片)), a high standard of quality is assured. Under the name of Futana you will be able to find knives of any profile made of stainless or semi-stainless steel. In addition, you will be able to find these blades with several different types of finishes; nashiji, kurouchi, damascus etc.