Hi Toroblanco!

Thank you! Well, latest months I can send lot less time into to it, but still here! Glad you are doing fine as well, and thank you so much for the compliments! Much appreciated!

Not a lot know about this, but what I've found is that 炭素鋼 = Tanso-kō = (Pure) Carbon Steel), I know Shigeyoshi-san did many experiments in developing
a steel trying to supersede Tamahagane and this 炭素鋼 was one of them. Also because Shigeyoshi-san was more into straight razors, I would think this one is made by him.

At https://historyrazors.wordpress.com/2016/12/08/iwasaki/, chapter 'Western razors – Straight Razors
‘Others’' there are a few more examples.

On the tang, there isn't maybe a Kamijo stamp?

Thanks for sharing!