Step 1 Bring a saucepan of salted water to a boil to blanch the peas. Blanch the peas for a minute to bring out the color (do this while the rice is cooking). Drain the peas and set aside. These can be folded into half the amount of cooked rice for the basic onigiri recipe.
Step 2 Divide the chopped umeboshi and use to fill 4 onigiri, forming the fresh pea rice around each onigiri.