Mix the brown sugar, soy sauce, and mirin.
Add the mixture to the fish slices and marinate for 30 mins to an hour, flipping a few times to coat both sides.
Save the marinade.
Cook skin side down on a non-stick pan over medium heat for 7 minutes. Flip and cook for another 5 minutes.
Add the marinade to the pan and cook for 2 more minutes.
Transfer the fish to a baking sheet, skin side down. Broil until desired crispiness.
Meanwhile, reduce the remaining marinade in the pan until it thickens, about 2 minutes.
Add 2 tbs of rice vinegar. Mix and cook until bubbly. Pour over salmon and serve.