Clean shirako by removing veins and membranes, then cut into bite-sized pieces. Prepare a bowl with water and 1 tsp salt, wash shirako in the salt water, and drain.

Boil water in a pot and blanch shirako in small batches. Transfer to ice water and pat dry with kitchen paper.

Slice nagaimo into thin strips.

Place a shiso leaf on the edge of a spring roll wrapper, add shirako and nagaimo (1/6 of each), sprinkle with salt, and roll tightly. Seal the edge with the flour-water mixture.

Heat salad oil to 170°C in a pot, add spring rolls, and fry until golden brown, turning occasionally.