If the aburaage you purchase don't come preseasoned, put the tofu in a bowl and pour boiling water over it to remove any excess oil, drain, and let cool. If they come preseasoned, you can skip this part. Cut each piece in half and gently open out each half into a bag
Mix the dashi stock, soy sauce, sugar, and sake together in a pan and bring to a boil, add the aburaage, and let simmer for 10-15 minutes until the liquid has almost all been absorbed. Remove from the heat, drain, and let cool. Press any remaining liquid out of the bags with a clean dish towel, they should be moist but not wet
Add the sesame seeds and seasonings to the sushi rice and mix them in. Fill the bag with the rice mixture. Serve at room temperature