Rinse the rice under cold water until the water runs clear.
Cook the rice according to package instructions or using a rice cooker for best results.
In a bowl, mix soy sauce, mirin, sake, sesame oil, sugar, and salt to create a marinade.
Toss the diced chicken in the marinade, ensuring each piece is well-coated. Let it marinate for at least 15 minutes.
Heat a pan over medium-high heat. Add the marinated chicken and cook until browned and cooked through, about 8-10 minutes.
Wet your hands with water to prevent the rice from sticking. You can moisten your hands with a mixture of water and a little salt. It adds flavor to the outside of the onigiri and can also help with shaping.
Take a small handful of warm cooked rice and place it in the palm of your hand.
Make an indentation in the center and place a spoonful of the cooked chicken.
Encase the filling with rice and shape it into a triangle or ball. Press gently but firmly to ensure it holds together.
Wrap the onigiri with a strip of nori. This adds a nice flavor and helps hold the rice together.
Repeat the process until all the chiken mixture is used.
Sprinkle sesame seeds on top of each Onigiri for an extra layer of flavor and crunch. Serve the onigiri warm or at room temperature.