Trim the roots of the mizuna and cut into bite-sized pieces. Roll a rolling pin over the aburaage to create a pocket, then cut each sheet in half along the longer side. Pour boiling water over the aburaage to remove excess oil and pat dry.

Roughly chop the peeled shrimp.

Place the nagaimo in a plastic bag and mash it with a rolling pin. Add the chopped shrimp, salt, and potato starch to the bag and knead to combine into a filling mixture.

Stuff 1/4 of the filling mixture into each piece of aburaage and seal the opening with a toothpick. Repeat to make 4 pouches.

In a pot, combine all the seasonings (mirin, soy sauce, dashi powder, and water) and bring to a boil. Add the stuffed aburaage pouches, cover with a lid, and simmer on low heat for 10 minutes.