The first thing I learned about Japanese cooking is that all the sauces were some combination of shoyu, rice vinegar, sugar, and mirin. This is a quick and easy meal that I made up. Shoyu is a Japanese soy sauce. It gives a much richer flavor than regular soy sauce, and tastes less salty. Mirin is Japanese cooking wine, made of rice wine. If you can't find any, just omit it, it will still taste wonderful.