In a rice cooker or pot add the rice, water (up to the 2 cup line if using a rice cooker), mirin, sake, soy sauce, and sesame oil. Stir to combine. Add the kombu on top and if using a rice cooker select the white rice function.
If not using a rice cooker, bring the liquid to a boil. Cover and reduce heat to low. Cook for 15-20 minutes or until the rice has absorbed all the liquid. Serve immediately.