Mix together soy sauce, sake, mirin, honey, and ginger in a small bowl.
Cut open the thick part of the chicken breast to even out the thickness.
With a fork, puncture the chicken breast all over. Using a butcher’s twine (cooking string), roll, wrap, and tie up the breast.
Heat oil on a frying pan and grill both sides of the breast. This is to keep the umami flavor.
Put the chicken breast and the marinade from step 1 into a Ziploc bag. Seal the bag, pressing out as much air as possible.
Place the bag inside the rice cooker and add hot water until the bag is fully submerged. The hot water should be enough to cover the chicken. The recommended temperature is below 158°F (70°C).
Close the lid, and keep warm for 2 hours.
Take the chicken out of the bag and let it cool. Once cooled, slice the chicken, and the chashu is ready!