Trim and separate the shimeji, tear the maitake, cut the carrot into small pieces and the aburaage into thin strips, and cut the chicken into small pieces. Rinse and drain the rice.
Mix the water, sake, and soy sauce in a bowl. Tear open the dashi packet and add the contents. Add the mushrooms, carrot, and aburaage and let sit for 10 minutes.
Put the rice in the rice cooker bowl and pour in the liquid and vegetables. Spread them evenly and lay the chicken on top without stirring.
Cook on the regular white rice setting (or the takikomi / mixed rice setting).
When done, fold everything together with a rice paddle. Serve topped with chopped green onion.