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1
Lay each cleaned cuttlefish mantle flat, inner surface facing up. Using a sharp knife held at a shallow angle, score the inner surface with light, parallel cuts 5 mm apart — do not cut through. This scoring reduces the mantle's tendency to curl during julienne cutting. The surface should show a fine crosshatch with no breach of the outer wall.
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2
Cut each scored mantle into planks 10–12 cm in length, working with the grain of the muscle fibres. Stack two or three planks with the scored surface facing upward. This is where the dish lives or dies: holding the blade at a 5° inward angle, julienne each stack into strips 1–2 mm wide with a single, decisive drawing stroke per strip. Uniformity governs both the noodle aesthetic and the textural contract of the dish — strips wider than 2 mm produce sliced squid, not ika sōmen. The finished strips should be translucent, glossy, and hold their length without breaking.
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3
Combine dashi, soy sauce, and mirin in a small saucepan. Bring just to a simmer, then remove from heat and cool completely over ice. The tsuyu should be pale amber and lightly fragrant — not dominated by soy. Taste: the dashi should be the primary register, with soy and mirin in clear support.
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4
Line wooden boxes or deep bowls with a generous bed of crushed ice. Drape the julienned cuttlefish strips naturally over the ice surface, allowing them to fall in loose, noodle-like coils. The strips should remain separate and glossy, not clumped. The entire assembly must remain below 5 °C; any warmth at this stage dulls the sweetness and begins texture degradation.
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5
Place freshly grated wasabi, shredded myoga, sliced green onion, and sudachi halves alongside the ice-set cuttlefish. Pour the cooled tsuyu into individual dipping cups. Serve immediately. The strips should be cold to the touch and uniformly translucent — any opacity or surface moisture indicates temperature failure.