To make teriyaki sauce combine soy, mirin and sake in mixing bowl. Stir in sugar, fresh ginger and Srircha sauce.
Pour about 1/2 the liquid into large zip lock bag. Add chicken thighs and shake. Marinate for about 30 minutes.
Meanwhile, place grill pan in oven, set to 400 degrees Fahrenheit. Once oven reaches desired setting, place marinated chicken in pan and cook for 10 minutes on each side, flipping once. To darken meat, set oven to broil and cook for 2 about minutes more.
Meanwhile, thicken sauce by pouring remaining liquid into a saucepan. Bring to a low boil, simmer and reduce, about 10 minutes. Remove chicken from oven, plate with juices from grill pan and serve with teriyaki sauce. Save extra sauce in sealable jar.