Shell shrimp, clean with potato starch, and rinse well. 

Slice scallops horizontally into two. Remove root ends of shimeji. Thinly slice mitsuba

In a small pot, put dashi and usukuchi shoyukoji, mix well, and heat.

Heat some water in a medium pot

In a small or medium mixing bowl, put egg, black pepper, sake, shiokoji and 1/2 tbsp of dashi + usukuchi shoyukoji (from pot).

Place egg mixture bowl in the warm water, and beat.

When egg mixture is warm (slightly higher than body temperature), remove from warm water pot, and continue beating until it makes peaks when whisk is lifted

In the meantime, when dashi and usukuchi shoyukoji boil, add shimeji, cover, and simmer until shimeji is soft.

Add shrimp and scallops, cover, and continue simmering until basically done (shrimp and scallops turn opaque).

Pour egg mixture over goodies in pot. Top with mitsuba, cover, and wait 1 minute (turn off heat after 30 seconds or so).  

It should look like this after a minute