Place chicken thighs in the bottom of your slow cooker.
In a separate bowl, mix together sugar, soy sauce, vinegar, salt, and ginger.
Pour over chicken.
Cook on low for 4 hours.
When the chicken has finished cooking, remove the thighs to a cutting board and roughly cut into bite-sized pieces (the chicken will mostly fall apart, you just want to break it up a bit).
Pour the sauce from the slow cooker into a small saucepan.
Bring to a boil.
In a small bowl, whisk together the water and cornstarch, then add the cornstarch mixture to the sauce.
Let the sauce boil on medium-low for about 5-10 minutes, until it has reached desired consistency (I like my teriyaki sauce thick and syrup-like).
Pour the sauce back over the chopped chicken and mix to coat.