Whenever I need to spruce up some blah japanese takeout, I make this:
Tiny spoonlet garlic salt
Tiny spoonlet furukake (i love seaweed and sesame seeds)
A few grinds of black pepper (mom used ground white pepper)
A few shakes rice vinegar (the sharpness of the vinegar should slightly outweigh the soy sauce)
A few heavy shakes soy sauce
A few shakes of Tapatío (or anything that brings the heat -- you want a little bite -- I have also used a couple jalapeño slices)
Mix it and then dump it (or sprinkle if you're civilized) over the blah dish. You will turn feral.
My mom's original was better but she used this as dipping sauce for everything.
In grad school I'd make a small jar and use it for lumpia, egg rolls, any kind of dumpling or picket full of meat.