In the slow cooker, add all ingredients except the corn flour and 4 tbsp water for the slurry.
Cook on low for 3-4 hours or high for 2 hours, or until the chicken is cooked.
In the meantime, cook up the required amount of rice, following the packet instructions.
Once the chicken is cooked take the breasts out and add the corn flour and water slurry to thicken the sauce. You can do this step in a pot if you want to speed up the process.
Using two forks, pull apart the chicken breast. Set aside to cool down, although serving it warm is quite nice as well.
Once the sauce has been thickened, add a few spoons of the sauce over the chicken.
To a bowl, in this order add rice, chicken, teriyaki sauce, kewpie mayo, then toasted sesame seeds if you are using them.