Defrost the edamame and remove the beans from the pods. Remove the pit from the umeboshi and mash it.

In a bowl, crack the eggs and whisk them. Add the dashi granules and silken tofu, then whisk until smooth. Mix in the edamame.

Line a heatproof container with plastic wrap, leaving extra wrap hanging over the edges. Pour the tofu mixture into the container and loosely cover with the excess wrap. Microwave at 600W for 3 minutes. Let it cool to room temperature, then refrigerate for 30 minutes.

In a saucepan, combine the sauce ingredients (sake, mirin, salt, dashi granules, and water) and bring to a boil over medium heat. Add the potato starch mixture to thicken, then mix in the mashed umeboshi. Let it cool and refrigerate for 30 minutes.