Slice the cucumbers very thinly into rounds, ideally with a mandoline. They should be almost translucent and slightly delicate-looking. Place in a bowl, sprinkle with 1 tsp salt, toss, and leave for 10 minutes. After 10 minutes, squeeze the cucumber gently but thoroughly by handfuls to remove excess water, then set aside. Do not skip salting and squeezing. It concentrates the cucumber flavor, keeps the salad crisp, and prevents the dressing from turning watery. That deliberate salting and squeezing draws real, considerable moisture out of the cucumber through osmosis, protecting the finished dressing from a real, specific dilution risk this genuinely thin, high-water-content vegetable would otherwise cause.

Place the dried wakame in cold water for 5–8 minutes until expanded and tender. Drain well, squeeze out excess water, and cut into bite-size pieces if the fronds are long. Wakame expands a lot. Do not over-soak or it can become too soft and lose its pleasant texture. That genuinely brief soaking window is calibrated precisely to fully hydrate the wakame while protecting it from the mushy, over-softened texture a longer soak would produce.

Bring a small pot of lightly salted water to a gentle simmer. Add the shrimp and poach for 1–2 minutes, just until pink, opaque, and curled. Drain immediately and cool under cold running water or transfer to ice water briefly. Drain very well. If the shrimp are large, cut them into bite-size pieces. If using very small salad shrimp, leave them whole. Do not boil aggressively or overcook. Shrimp for sunomono should stay tender and juicy, not firm and rubbery. That immediate cold-water shock, right after poaching, halts the shrimp's own carryover cooking precisely at the point they're just done, protecting them from the tougher, rubbery texture continued residual heat would otherwise cause.

In a small bowl, whisk together the rice vinegar, sugar, ½ tsp salt, soy sauce if using, and sesame oil if using. Whisk until the sugar and salt dissolve completely. Taste: the dressing should be bright, lightly sweet, and clean, not harshly acidic. That thorough whisking, continued until both the sugar and salt have genuinely dissolved, is what produces a real, smooth dressing rather than one carrying undissolved grains that would sit unevenly once tossed through the salad.

In a mixing bowl, combine the squeezed cucumber, wakame, cooked shrimp, and most of the pickled ginger. Pour over the dressing and toss gently until evenly coated. Let the salad sit for 10–15 minutes in the refrigerator before serving so the cucumber and wakame absorb the dressing. That brief, chilled resting period gives the dressing genuine time to actually soak into both the cucumber and wakame, rather than simply coating their surfaces without ever being absorbed.

Transfer to a serving bowl and scatter over the white sesame seeds, black sesame seeds, and remaining pickled ginger. Serve chilled or cool. Reserving a final portion of pickled ginger specifically for this finishing stage, rather than folding it all in earlier, keeps that bright, sharp element genuinely visible and distinct right at the surface of the finished salad.