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1
Prepare the bonito: trim the fillet into a neat block, skin on. Soak the sliced onion in ice water until required. Fill a large bowl with iced water and set it immediately beside the fire station. Both must be ready before the straw is lit — the sequence from flame to ice bath admits no delay.
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2
Ignite the rice straw bundles. Allow the flame to establish and reach full intensity — the contact point burns at 800–1000 °C. Hold the bonito block on a skewer or heat-proof tongs, skin side facing the flame first. Sear each surface for no more than 30–60 seconds per side, rotating through all four faces and finishing with the skin. The surface must show clear caramelization and a definite char; the straw smoke must penetrate. This step decides the dish: too brief and the Maillard crust does not form; too long and the raw interior is lost. The dish lives or dies in this minute over the straw.
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3
Transfer the seared block immediately into the iced water. Hold submerged for 30 seconds only — long enough to arrest cooking at the 2–3 mm seared layer, not long enough to chill the core. Remove and pat thoroughly dry.
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4
Slice the block across the grain into pieces 8–12 mm thick. Each slice must show a distinct seared band of caramelized flesh at the perimeter enclosing a raw, translucent red interior. Thin slices are a failure — the raw core is the definition of tataki.
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5
Arrange the slices on a cold plate. Drain the ice-water onion and shake dry; lay alongside the fish. Place grated garlic — the Kochi standard — beside the fish. Pour ponzu over and around. Taste: the acid of ponzu must cut the char and lift the raw bonito without overwhelming either.