Like miso paste, soy sauce originates from hishio. It took longer for soy sauce than miso until town folks started to adopt it as a seasoning for sashimi for example. It seems its popularity picked up slowly from the early Edo period only (17th century). It was then referred to as tamari.
The preferred seasoning for sashimi, which did eventually decline when soy sauce took over, was irizake, and I was happy Soma san from the must-go-to sake bar The Hangar prepared some, to accommodate our Tai (seabream) sashimi. It reminded me of a great meal and lesson by Jihei Isawa at Katsuyama. Jihei’s recipe for irizake is: 1 bottle (1.8 liters) of Katsuyama Genroku sake, 12 umeboshi (marinated salted prunes), boil to a 60% reduction, add katsuoboshi (bonito flakes). Unlike soy sauce, irizake was difficult to conserve… If you do not have Genroku sake (a recipe from early Edo), try with a relatively sweet and full bodied sake with nice acidity, or go for your “usual sake”, ideally blended with some kijoshu (sake brewed from sake).
By the way, nobility and samurai were only eating sashimi of white fish until the late Edo period. Soma san had enhanced flavor and look with grated freeze-dried plum.