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1
If using sweetened soy glaze, combine soy sauce and mirin in a small saucepan over low heat and reduce briefly until slightly syrupy; set aside warm. For plain soy, use soy sauce directly. Allow kirimochi to reach room temperature fully — a frozen or cold centre causes uneven heating and risks explosive steam expansion during grilling.
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2
Arrange kirimochi on a wire mesh grill set directly over a medium gas flame, or in a toaster oven, leaving clear space between each piece to allow for expansion to approximately 150% of original size. Grill 5–8 minutes per side. The mochi is ready when the surface blisters and puffs dramatically, the exterior is crisped and lightly charred in places, and the interior has become soft and molten — press the surface gently: it should yield with immediate resistance, not feel firm throughout.
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3
This is where the dish lives or dies. The moment the mochi comes off the heat, brush the soy glaze generously over all surfaces while the exterior remains intensely hot. The residual heat caramelises the soy against the blistered surface; soy applied before grilling is complete burns without caramelising, and soy applied to a cooled surface remains raw seasoning rather than a glaze. The coated surface should darken and take on a faint sheen within seconds.
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4
Immediately — within 30 seconds of soy application — wrap each glazed mochi piece in a half-sheet of yaki nori, pressing firmly so the nori adheres to the hot, slightly tacky soy-coated surface. Nori absorbs moisture rapidly: beyond 30 seconds the sheets transition from crisp and papery to soft and chewy, and the textural contrast that defines the preparation is lost. Serve at once.