Need to know the logistics of Japanese swordsmithing
I am thinking up a backstory for an odachi of legendary status, made of a fictional metal that is impossible to break, melt, or even sharpen.
Assuming it has similar properties to Japanese steel, with the inability to be reheated, how long would this steel need to stay soft in order to make the katana in one night by a true master of the craft and no less than a dozen high level apprentices to assist?