Dark soy sauce "Blue Dragon" brand (widely available in uk supermarkets)
Oak smoke.
Popped some in a small vessel, (actually a polyprop drink lid for a thermal steel lined mug) probably around 25ml & stuck in to smoke for around 6 hours overnight then rested.
Again like the marmite, it appears to take well & lowers the saltiness on your tongue whilst pushing forward a developed smokey tang & aftertaste.
I usually have a few days a month / one day per week where I simply eat rice with smattering of soy, although I haven't done a big qty will make up some rice & see how it fares over a meal & also to go with sushi.
I'm really eyeing up that salmon for nigiri now, but first will have to brine some turkey.