Well, OK I'll open up the kimono a bit more about this mystery - it is a man not a woman who does this work
I wish I could tell you more about the maker and the steel, but honestly, I have not been given the information either. Believe me, this is a challenge for me too, but I understand their reasoning. He desires privacy in the matter lest his competitors use the same steel or worse yet, either go around him or put him in a position where he winds up cranking out knives for 'them'. He is just protecting his position.
There was a pretty extensive review done of a Nubatama yanagi. There is an upcoming long term review of a 240 ryoba or gyuto from a customer who has had one for a period of time. I've also used a few of them extensively. Edge retention is exceptional. Ease of sharpening is also exceptional, but rarely needed. I've been able to retain my edge for home use for over a year with only stropping on compounds. The double bevel knives are clad and the core reacts like a carbon steel, developing a patina. A number of chefs in Kyoto have switched over from their Aritsugu knives to Nubatamas and are quite pleased with it's performance. The final finishing is done by a sword polisher - and before anyone asks, he too won't say which natural stones he uses. Yes there is a pattern here. Their perspective is that the knives' performance is what will sell the knife and the steel is the concern of the knifemaker not the customer. I KNOW that we steel junkies don't agree with this at all and 'Inquiring minds want to know'.