Bake salted salmon at 400F degree in a toaster oven for 25 minutes and break the cooked salmon into flakes.
Pit umeboshi and cut it in half (optional)
Moisten katsuobushi with soy sauce.
Let the cooked rice cool a little bit until you can hold rice without burning your hands. However, do not let the rice completely cool down.
First wet both of your hands with water in order to keep the rice from sticking to your hands.
Then put some salt in your hands and rub to spread all around.
Scoop out a handful of warm rice (about ½ cup) into one hand.
Using the other hand, make an indentation in the rice.
Place one kind of filling (about 1 tsp.) inside.
Press the filling into the rice.
Then use your hands to mold and press the rice around the filling to gently form the rice into a triangle.
Form the bottom with your left hand and the top corner with your right hand. I use three fingers (thumb, index finger, middle finger) to cover the area to make a nice triangle shape. Pressing the triangle into the palm of your left hand, squeeze each corner of the triangle with your right hand. Your hands should be just firm enough so the onigiri doesn't fall apart. You don't want to squeeze the rice too tight.
Also, while you squeeze onigiri firmly with both hands, your left hand has to press onigiri in order to keep a nice form. The left photo shows before squeezing and right photo shows after.
Place a little bit of each filling on top of onigiri so we know which kind it is. Before you serve, wrap the onigiri