Instructions:
1. Gather all the ingredients.
2. Soak bamboo skewers in water for 30 minutes.
3. In a small saucepan, add the mirin, soy sauce, sake, water, brown sugar, and the green part of 1 scallion, and bring it to a boil over high heat. Once boiling, reduce the heat to low and simmer, uncovered, until the liquid is reduced by half. It will take about 30 minutes. The sauce will be thicker and glossy. Let it cool to room temperature before using. Reserve 1/3 of the sauce in a small bowl for final coating.