Roll a chopstick (or another blunt-edged object) over the aburaage sheets to break down the fibers and make them easier to open.

Blanch the aburaage sheets in plenty of boiling water for 1 to 2 minutes to remove excess oil, then drain.

Rinse the aburaage sheets in water to cool, then press them firmly by hand to remove the excess water.

Cut the aburaage sheets in half and gently open them into pockets.

Arrange the aburaage pockets in a radial pattern in a saucepan, leaving the center empty.

Pour the dashi, sake, soy sauce, mirin, sugar, and salt into the center of the saucepan. Place a drop lid or a piece of parchment paper directly on top to keep the pockets in place.

Simmer over medium-low heat for about 20 minutes, pressing down on the drop lid from time to time to distribute the liquid evenly. Adjust the seasoning if needed.

When only a little liquid remains, turn off the heat and let the aburaage cool in the saucepan for a few hours so it can absorb the seasoning.

Cook the Japanese rice with slightly less water than usual.

Mix the rice vinegar, sugar, and salt to make the sushi vinegar, then pour it over the hot rice.

Gently fold the rice with a slicing motion using a spatula, then add the sesame seeds and sanshō peppercorns.

Shape the vinegared rice into small oval portions.

Fill the aburaage pockets with the portions of vinegared rice.

Serve with pickled ginger and shibazuke, to taste.