Combine all ingredients (except chicken) and stir until sugar is dissolved.
Add the chicken thighs to the slow cooker and pour the sauce over the top.
Cook on high heat for 3 hours, or low for 6 hours. Cooking on low heat results in more tender, juicy chicken.
Remove the chicken from slow cooker and place on a lined baking sheet.
Place it under the broiler to allow the skin to crisp. I try to place it at least 12 inches from the heat so the skin crisps more evenly. It should take about 3-4 minutes, but all broilers are different. Be careful to watch it to ensure it doesn't burn.
Garnish with sesame seeds and serve with steamed white rice and extra teriyaki sauce (below) on the side.
To Thicken the Teriyaki Sauce:
Pour 2 cups of the cooking liquid in a sauce pan and heat to simmering. Mix 1 tablespoon of cornstarch with 1 tablespoon of water to make a cornstarch slurry.
Slowly pour the cornstarch slurry into the saucepan, while continuously stirring. The sauce should thicken and become glossy.
Notes
I recommend using low heat instead of high as the chicken comes out more tender and juicy. However, if you're in a time crunch, high heat will work.
Be sure to watch the chicken while broiling it to ensure it doesn't burn.
Add additional cornstarch slurry to the sauce if it's not thick enough. Make it as thick or thin as you like.