While the rice cools, combine 1 tsp salt and 1 cup of warm water. Stir until the salt dissolves completely and set aside.
When the rice is cool enough to handle, wet your hands with the salt water and scoop out ¼ cup of warm rice. Shape the rice into your desired shape.
If adding mix-ins, mix the ingredients with the rice in your hands and then shape.
If adding filling, make an 1 inch indent in the center of the rice, and add the filling into the indent. Then add a bit of rice over top of the filling to seal, and form into your desired shape. Use more salt water on your hands as needed.
If you want to sear your onigiri, heat a heavy bottomed pan over high heat. Coat the base of the pan with a thin layer of neutral, high smoke point oil. When the oil is hot, add the onigiri to the pan and allow to sear undisturbed until crisp, about 2-3 minutes. Sear on one side or both sides. If the onigiri is sticking when you try to flip it or remove it from the pan, it simply has not seared enough. Give it a little more time!
Roll your onigiri in toppings if you like. If eating right way, you can add your nori wrappers now. If you are storing the onigiri, wrap individually in plastic wrap, then wrap in a thick kitchen towel and store in an airtight container in the refrigerator. The towel with protect the rice from getting too cold and hard. Add the nori just before eating so it doesn’t get soggy!