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1
Prepare the binchotan charcoal well in advance. The coals must be uniformly white-ashed and glowing at a moderate, even heat — not the highest temperature the fire can reach. Hold your palm 15 cm above the grill: it should be comfortably warm but not scorching. Uneven or excessive heat is the source of every common failure in this dish.
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2
Examine each whole, ungutted ayu for the suika-ka — the watermelon or cucumber fragrance that rises from the skin and gills. This is the fish's quality signal and the proof of wild, algae-fed stock. A fish without it is from aquaculture and will not deliver the dish's defining character. Pat the fish dry.
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3
Skewer each fish in the sugata-yaki (姿焼き) pose: pass a long metal skewer through the fish in a living swimming curve — head angled up, body gently arched, tail swept to one side. The curve must hold so that all surfaces of the fish receive even charcoal exposure. A loose or straight skewer will collapse the presentation and cook the fish unevenly.
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4
Salt the fish. Apply a heavy, deliberate coat of coarse sea salt to the tail fin and all other fins — these surfaces face the highest radiant heat and will burn to ash without adequate salt protection. Apply a noticeably lighter, even coat to the body. The belly and the intestinal region need only a dusting; ayu's delicate flavour is immediately overwhelmed by excess salt on the flesh.
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5
This is where the dish lives or dies. Grill the skewered ayu over moderate binchotan for 12–15 minutes, turning once at the midpoint. Maintain the moderate heat throughout: too fierce a fire burns the skin before the interior cooks; too gentle a fire steams rather than grills. Watch the skin — it should progress steadily to a golden colour with a faint, irregular blister forming across the surface. The charcoal smoke rising through the fish carries the algae character upward into the flesh.
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6
Test for doneness: the skin is golden and lightly blistered across its full surface. Press the thickest part of the body gently with a finger — the flesh should yield with resistance, not feel soft or raw at the centre. Draw one tine of a fork or skewer along the spine at the shoulder: the flesh should release cleanly from the bone without tearing or clinging.
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7
Serve each fish immediately, whole, in its skewered pose or with the skewer drawn cleanly out, head and tail intact. The head is not a garnish — the cheek meat is prized and the presentation is inseparable from the dish. If tadezu is served alongside, offer it in a small dish. The fish is eaten from head to tail; the intestines (harago), if left in, are consumed as the dish's most sophisticated element.