Drain the oil from the aburaage (quickly pour some hot water over it) and cut into large pieces.
Put the dashi, sugar, mirin, and sake into a pot and turn on the heat. Once it comes to a boil, add the aburaage and cover with a drop-lid. Simmer over low heat for 10 minutes.
Pour in the usukuchi soy sauce and simmer until the liquid has mostly evaporated. Occasionally flip the aburaage over as the liquid boils down. Turn off the heat. Leave it as-is until it cools so that the flavors settle.
Story Behind this Recipe
I don't really like the rich-flavored aburaage sold in supermarkets or shown in cookbooks, so I made this lightly flavored type. I wrote this recipe from memory.
There aren't really any hints. First put the udon and mentsuyu in the bowl and then place the aburaage on top.