Carefully remove the tentacles and innards from the squid.

Insert a knife into the body, and cut it open on the opposite side of the cartilage. Rinse in water and remove any viscosity.

Remove the fin. Do this carefully so as not to remove any of the flesh from the body.

Peel off the skin from where the fin was removed. The skin should come off easily if the squid is fresh.

Trim off the edges. Save the trimmed off parts to use with the innards and fin in a different dish.

Trim the flesh into a rectangular shape. (These trimmings can be used for sashimi, or added to the innards and fin for a different dish.)

Score the outer surface of the squid evenly with 5 mm spaces in between each cut. The depth of the cuts should be about 1/2 the thickness of the flesh. Be careful not to cut too deep.

Place the sheet of nori seaweed on top of the inner surface of the squid, then roll the squid parallel to the score marks. With the sealed side down, slice the roll into 1 cm thick pieces.

Place shiso leaves on a plate, then arrange the squid on top. Add a dab of wasabi, then it's ready to serve.