In fine-mesh strainer, rinse rice under cold running water until water runs clear. In small saucepan, combine rice and 1 1/2 cups water; bring to simmer over medium-high heat. Reduce heat to low; cover and cook for 12 to 15 minutes or until rice is tender and liquid is absorbed. Let stand for 5 minutes.
Meanwhile, stir together vinegar, sugar, and salt; toss with rice. Cool completely. With wet hands, shape 1/4 cup rice into a patty. Place about 1 tbsp chicken tossed in teriyaki sauce in the center; shape rice around chicken to enclose filling, forming ball. Repeat with remaining rice and chicken. Roll balls in sesame seeds; garnish with chives and serve with soy sauce for dipping (if using).
Tip: Add 1/4 tsp wasabi paste to soy sauce for a spicy kick if desired.