Cut the chicken thighs and set them aside.
Whisk the teriyaki sauce ingredients in a bowl.
Add the chicken to the sauce and stir through to coat.
Set up the Instant Pot. Add ½ cup of chicken stock or water to the bottom.
Add the chicken and all the marinade. Spread the pieces evenly.
Secure and lock the lid. Set to Pressure Cook for 10 minutes on HIGH. The Instant Pot should take about 5-7 minutes to come to pressure. Once cooked, natural release the pressure for 5-10 minutes and then quick release the remaining steam. Then, open the lid.
Prepare the sides in the meantime. You can cook the rice ahead of time (also in the IP) and boil or steam broccoli or make a simple cabbage salad.
Once the timer is done, open the lid.
Add the additional tablespoon of sugar and press the Saute function (Normal mode) and allow the sauce to come to a boil. Cook on simmer, stirring frequently until half of the liquid has evaporated and the sauce has thickened quite a bit.
Note: Taste the sauce to make sure sugar and salt are balanced, you can add a little more soy sauce or salt or sugar as needed. If it feels like it needs a little more acidity, you add a tiny splash of rice wine vinegar or lemon juice.
Finish with a teaspoon of butter (for shine and richness) and if needed to thicken the sauce further, make a flour and water slurry and stir it into the sauce right at the end. Press Cancel to stop the Saute function.
Optional: To make a slurry, whisk the cornstarch with 2 tablespoons of water until smooth.
Garnish with diced green onions and sesame seeds.