Remove a square of plastic wrap from the roll, and place it in the small cup, bowl, or ramekin. It doesn’t have to perfectly line the inside of the dish, but the closer you can get, the better.
Dip your fingers into the bowl of water, and sprinkle it on the portion of plastic wrap inside the dish.
Use the salt shaker to add some salt to the water on the plastic wrap. Use your fingers to disperse it evenly throughout the inside. If any excess is pooling up at the bottom, flip the wrap and dish over together over the sink and shake gently or pour it out.
Use a rice paddle or large spoon to add your cooked, warm (not hot!) rice to the dish until it reaches the top. Do not press down.
Use your thumb to hollow out a space in the middle of the rice. Your thumb should only go about halfway in. Widen it until you have a diameter of about ¾”.
Add your smoked fish (or another filling) to the pocket. Cover it gently with an additional clump of rice.
Pull the loose edges of the plastic wrap together to meet over the center of the rice in the dish, and lift up the rice in the plastic wrap from the dish. Holding the top of the plastic wrap in one hand, use the other to spin the rice around. The goal is to remove the air and compress the rice together. You may have to adjust the top slightly to ensure all the air is out.
When the top is firmly sealed and the rice ball has compacted well, use your thumb and two forefingers to press the ball into a triangular shape. As you work on shaping the sides, you’ll occasionally have to use your palms to pat the faces (front and back) back down.
Gently remove the rice from the plastic wrap, and set it aside. If you’re not using seasonings or seaweed, you’re done! If you’re using seaweed: use a sharp knife to cut a rectangular strip of nori about 3” long. Set aside.
If you’re using furikake or black sesame seeds, sprinkle them in a line on your plastic wrap. Gently press one side of the onigiri to it; if your rice is cooked properly, it will stick easily. Repeat this for another side.
Apply the nori to the front of the onigiri, using two fingers to gently press it onto the rice, with the edge sitting just below the vertical halfway point of the triangle. If the nori’s not sticking well, you can use a finger to gently brush it down with a small amount of water. Continue to press it along the bottom side, then to the back of the onigiri.
Hold by the nori strip, if you added one, and enjoy!