Cook the rice

• Rinse the rice until the water runs clear.
• Cook the rice with the water in a covered saucepan until tender and fluffy.

Season the rice

• Mix the rice vinegar, sugar and salt until dissolved.
• Fold the seasoning into the warm rice and let it cool slightly.

Make the tuna mayo filling

• Drain the tuna well.
• Mix the tuna with the mayonnaise in a bowl.

Shape the onigiri

• Wet your hands and take a portion of rice.
• Press a hollow in the center, add the tuna mayo filling and close the rice around it.
• Shape into a triangle or ball, pressing firmly.

Wrap and serve

• Wrap each rice ball with a strip of nori.
• Serve immediately or keep chilled until eating.