Begin by thoroughly rinsing the rice in a mesh strainer under cold water until the water runs clear. Once clean, combine the rice and 4 ½ cups of water in a large saucepan. Set the heat to high and bring the mixture to a rolling boil, stirring occasionally to prevent sticking. After boiling, reduce the heat to low, cover the saucepan, and let the rice simmer gently for 15 to 20 minutes, or until all the water is absorbed. Once done, allow the rice to rest, covered, for an additional 15 minutes to steam and become tender. Set the rice aside to cool.

In a small bowl, mix the remaining 1 cup of water with the salt. This solution will be used to dampen your hands before shaping the rice. Divide the cooled rice into 8 equal portions. For each onigiri, take one portion and divide it in half.

Shape the first half into a rough ball and create a small indentation in the center. Fill this hollow with a generous teaspoon of bonito flakes. Place the second half of the rice over the filling and gently press the two halves together to enclose the bonito inside. Shape the rice into a compact triangle, being careful not to press too hard. Wrap a strip of nori around the bottom edge of the triangle and finish by sprinkling the top with sesame seeds. Repeat the process with the remaining rice portions to make 8 onigiri in total.