Gather all the ingredients. For making onigiri, please use hot, freshly cooked Japanese short-grain rice.

To make the tuna salad, drain ½ (5-ounce) can albacore tuna. Transfer to a bowl and break up the tuna chunks into small flakes. Add 1 Tbsp Japanese Kewpie mayonnaise and ¼ tsp soy sauce. Mix well to combine.

Let the freshly cooked 2¼ cups cooked Japanese short-grain rice cool slightly in a large bowl or tray so it's easier to handle.

To keep the rice from sticking to it, wet an onigiri mold and lid in a bowl of water and shake off the excess water. Sprinkle salt in the moistened mold.

Fill it halfway with rice, making sure to tuck the rice into the corners. To the center, add a spoonful of tuna mayo filling (about 1–2 tsp). Add more rice to cover the tuna mayo and fill the mold to the top edge.

Sprinkle the top of the rice with a bit more salt. Cover with the lid and push down firmly. You should feel a slight resistance as you compress the rice; if not, add a bit more.

Remove the lid, flip the mold over, and push the 'button' to release the rice ball onto a plate. Repeat to make the remaining onigiri.

Place a piece of plastic wrap in a rice bowl or any small bowl and sprinkle it with Diamond Crystal kosher salt. Add about ⅓ cup rice.

Create a small indentation in the center of the rice, then add a spoonful of tuna mayo, about 1–2 tsp. Add another ⅓ cup rice on top to cover the tuna mayo completely. Sprinkle the rice with more salt.

Gather the corners of the plastic wrap and twist the plastic to tighten it around the rice. Gently press the rice with your top hand in a 'mountain' shape to form a triangle corner.

Cut 1 sheet nori into thirds. Wrap the onigiri from both sides with a strip of nori seaweed, leaving the top corner exposed. Serve warm or at room temperature.