Prep the fish. Pat the sea bass completely dry with paper towels — this is crucial for browning. Score the skin in a crosshatch pattern about ¼ inch deep, being careful not to cut into the flesh. Season both sides lightly with salt and pepper.
Make the glaze. In a small bowl, whisk together the miso paste, mirin, soy sauce, sugar, rice vinegar, and grated ginger until smooth. If your miso is particularly thick, add 1 teaspoon of water to loosen it slightly.
Sear the fish. Heat oil in a large skillet over medium-high heat. Place the sea bass skin-side down in the pan (it may stick at first — that's fine). Cook undisturbed for about 4 minutes until the skin is golden and crispy. Flip carefully using a thin spatula or two forks.
Glaze and finish. Brush the top side generously with half of your miso glaze. Reduce heat to medium-low and cook for another 3–4 minutes, brushing occasionally with remaining glaze. The fish is done when it reaches an internal temperature of 125°F (you can check by inserting a thermometer into the thickest part). The flesh should be opaque but still slightly translucent near the bone.
Rest and serve. Transfer to a plate and let rest for 2 minutes — this allows juices to redistribute. Serve with steamed rice, drizzling any remaining pan glaze over top.
