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1
Place the dried hijiki in a large bowl and cover generously with cold water. Soak for 30–60 minutes — cold water only; hot water compromises texture. Drain, rinse twice under running water, and drain again. The strands will have tripled or quadrupled in volume and shifted from stiff black twigs to soft, yielding threads. Any strands that remain hard or wiry require more soaking time.
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2
Blanch the abura-age sheet in boiling water for 30 seconds to purge excess oil. Drain, press gently, and slice into thin strips. Cut the carrot into fine matchsticks of similar length to the reconstituted hijiki strands.
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3
Heat the sesame oil in a medium saucepan or shallow braising pan over medium heat. Add the abura-age strips and carrot matchsticks and sauté briefly until the carrot is lightly coated in oil and the pan is fragrant with sesame. Add the drained hijiki and turn to coat, sautéing for one further minute until the strands glisten.
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4
This is the step where the dish lives or dies. Pour in the dashi, mirin, soy sauce, and sugar. Stir once to distribute. Bring to a gentle simmer over medium-low heat and braise uncovered, stirring occasionally, until the liquid is almost completely absorbed — the hijiki should be moist, with sauce clinging to each strand, but the pan must not be soupy nor dry-scorched. This takes approximately 15–20 minutes. Taste midway: the balance should be sweet-savoury with the mineral depth of the hijiki coming through; add a small measure of soy only if necessary.
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5
Add the podded edamame in the final 3 minutes of braising only. Fold them in gently. They are done when they are heated through, still bright green, and retain slight resistance at the bite.
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6
Remove from heat. Taste once more for seasoning. Transfer to a serving dish or individual small bowls and allow to cool to room temperature before serving — hijiki no nimono is one of the few Japanese dishes that genuinely improves as it cools, the sauce fully penetrating the strands as they rest.