Cut each lemon in half, slice off the top. Scoop out the segments and place the sliced off top back into the lemon half to create lemon bowl. Squeeze out juice of the scooped out segments and set aside. Remove any cartilage from crab, break coarsely, then season with the lemon juice. Soak the celery slices in cold water for 4 or 5 minutes, then drain. Set aside celery leaves if you would like to use it for garnishing later. Soak fresh or dried wakame in measured water until expanded, about 10-15 minutes, then cut into pieces ranging between a half inch and one inch square (Dried and pre-cut wakame usually comes in this size). In a colander, pour boiling hot water over wakame to clean and set the fresh green color.
Mix dressing (soy sauce & lemon juice & mustard) ingredients together, spoon into premade lemon bowls and serve.