Turn your Instant Pot to the saute setting. (See your manufacturer's guide for detailed instructions on how to use your instant pot.)
Add the water, soy sauce, mirin, honey, sesame oil, garlic and ginger to the instant pot and stir.
Place chicken thighs in the instant pot, they should be immersed in the liquid.
Close the lid (follow the manufacturer's guide for instructions on how to close the instant pot lid). Set the Instant Pot to the Poultry setting and set the timer to 8 minutes.
Once the Instant Pot cycle is complete, wait until the natural release cycle is complete, should take about 10 minutes. Follow the manufacturer's guide for quick release, if in a rush. Carefully unlock and remove the lid from the instant pot.
Remove chicken from the instant pot and place on a baking sheet.
Switch the Instant Pot to the saute setting (do not put the lid on). Transfer the chicken to a bowl using a slotted spoon. Thicken the sauce by stirring the cornstarch with 3 tbsp cold water and stir it into the sauce. Cook for 5 minutes on the Saute mode, stirring occasionally. Turn off your Instant Pot by pressing the cancel button.
Brush the chicken with the sauce, then place the baking sheet under the broiler until browned, for about 5 minutes.
Garnish the chicken with sesame seeds or green onions. Serve over rice.