Onigiri 3 Ways 

1. Cover the rice with cold water in a medium bowl, swirl the rice, pour off the water and repeat until the water is clear, 4 or 5 times. This will help to remove the excess starch. Drain the rice and transfer to a medium saucepan. Add 1 3/4 cups cold water and bring to a boil over high heat, then reduce the heat to low. Cover with a lid and cook for 15 minutes. Remove from the heat and let stand, covered, for 15 minutes. Remove the lid and fluff the rice with a fork. (Alternatively, cook the rice in a rice cooker.) Transfer the rice to a large glass bowl and let cool slightly. Using a glass bowl will let you see if there's any pooling at the bottom when the vinegar is added in the next step.
2. Stir the sugar with 1 tablespoon hot water in a small bowl until the sugar has mostly dissolved. Add the vinegar and stir until combined. Drizzle over the rice and fold gently with a wooden spoon or rubber spatula. Cover the bowl with a clean kitchen towel and let the rice cool slightly. This is a good time to make the filling of your choice. 
3. To assemble each onigiri: Lightly dip your fingertips in a small bowl of warm water then rub your hands together to wet them. Scoop just over 1/3 cup of the rice and gently flatten into a triangular patty about 1 inch thick and 3 inches wide on each side. Using your thumb or index finger, make a little indentation in the center and fill with about 1 tablespoon of the tuna mayo or egg salad, or 1 1/2 teaspoons of the umeboshi paste. Cover the filling with 1 1/2 tablespoons of the remaining rice, pinching the sides of the onigiri to completely enclose the filling. Be sure to gently pack the onigiri, without too much pressure, otherwise the rice will become too dense.  
4. Optional for finishing: For the tuna mayo onigiri, gently roll all sides in the furikake. For the umeboshi onigiri, dab a bit of the remaining umeboshi paste on one tip of the triangle. For the egg salad, sprinkle some of the togarashi on one tip of the triangle. 
5. When ready to serve, place the onigiri in the center of a nori strip and wrap it, tucking the ends into the sides of the onigiri. Enjoy immediately to prevent the nori from becoming soggy. (The onigiri can be made ahead of time but do not add the nori until ready to eat.) 
6. To help differentiate the fillings, you can wrap or decorate the onigiri with the nori in different ways. For example, fully wrap the ones with tuna mayo; add a square piece of nori to the ones with umeboshi; and wrap a narrow strip around the ones with egg salad.  

Tuna Mayo:

1. Combine the tuna with the mayonnaise, soy sauce and sriracha in a medium bowl. Using a rubber spatula, fold until well combined. Use right away or refrigerate in an airtight container for up to 2 days. Makes a heaping 1/2 cup.

Umeboshi Paste:

1. Combine the umeboshi with the sugar and honey in a small bowl. Mash with a fork until a paste forms. Use right away or refrigerate in an airtight container for up to 2 days.

Egg Sando Egg Salad:

1. Place the eggs in a small saucepan, cover with cold water and add the vinegar. Bring to a boil, cover and remove from the heat. Let stand, covered, for 6 minutes. Drain and rinse under cold water, then peel.
2. Finely chop 2 of the eggs and transfer to a medium bowl. Add the mayonnaise, mustard, salt, white pepper, and togarashi and fold until well combined. Roughly chop the 1 remaining egg, add it to the bowl, and fold until just combined. This will give the egg salad two different textures, which is traditional in Japanese egg salad sandos. Use right away or refrigerate in an airtight container for up to 2 days. Makes 3/4 cup.