This was purchased directly from Mr. Mukai, also known as Genkai Masakuni, at his workshop. Initially, it was forged and polished, but I had it finished with a double mirror polish by Mr. Shimizu, a sharpener in Sakai. It's a very rare item, with a hamon (temper line) applied to the spine, creating a double yakiba (hardened edge) pattern on both the shinogi (blade ridge) side and the spine side. I think it's a super rare item that's hard to find! Recently, Mr. Mukai passed away, so it will undoubtedly become even more valuable in the future. Made by Genkai Masakuni, Water Hon-yaki (true heat treatment) with Shirogami #1 steel. Since it's fully mirror-polished, it's great for collections! It's a fugu (pufferfish) knife with a thin edge, so its overwhelming sharpness makes it highly recommended for slicing regular sashimi as well. In terms of specifications, I believe it's an exceptional piece! It has been stored with a genuine natural whetstone and has been sharpened, so it's practically unused. I hope it goes to someone who will cherish it.