Cook the rice per the instructions on your rice package.
While the rice is cooking, add the bonito flakes, soy sauce, and sesame seeds into a mixing bowl and combine until the liquid has absorbed into the bonito flakes.
Once the rice is done cooking, cut the nori sheet into three evenly sized strips. Be sure to use high quality, fresh nori so it will be nice and crispy.
When you're ready to assemble the onigiri, wet your hands and rub a little bit of salt on them prior to handling the rice. This helps to season the rice and keep it from sticking to your hands.
Then take a handful of rice into your hand and flatten it slightly, making a small well in the middle for the filling.
Add a spoonful of the bonito flake mixture to the well in the middle of the rice and cover with another small handful of rice.
Then form the rice into a triangle shape by cupping your hands and gently pressing the rice with your palm and fingers (see video for more detail). Most beginners tend to press too hard when shaping the rice. Instead, you want to gently use your hands to form the rice into a triangle shape.
Next, wrap a strip of nori around the onigiri and press together where the nori strips overlap. Wetting the nori slightly where it overlaps helps it to stick better
Serve and enjoy!