This is what I often do with my very fresh fish. It requires just 10 minutes of cooking/working time. Salt the fish (with skin) and cook it in the oiled skillet, skin side down, until the skin is crisp and the fish is cooked about 60 percent. Turn the fish over and cook until it is cooked through, but not over-cooked. In order to cook the fish medium-rare inside you have to start with a very fresh fish, but not an ordinary fish for safety.
Transfer the cooked fish to the serving plate. Throw in a piece of butter to the fish cooked skillet and cook until it melts. Add little shoyu (soy sauce) and freshly squeezed lemon juice to the skillet and cook until it bubbles. I often add concentrated dashi stock to this mixture. It really boost the umami in the sauce. This is the sauce for my fish. Delicious sauce.
Use the good quality butter and shoyu (soy sauce) to match that of fish. My butter is Isigny from Normandy, and my shoyu is Kishibori shoyu is from Shodo Island, Japan.