Rinse the Japanese rice under cold water until the water runs clear. Place in a medium saucepan with 2 cups water. Cover and cook on low-medium heat for 30 minutes until tender. Remove from heat and let steam for 10 minutes.

Transfer cooked rice to a large sheet pan. Spread in a thin layer. Sprinkle rice vinegar, sugar, and salt over the rice. Using a rice paddle, fold the seasoning into the rice and spread out to cool to room temperature.

Drain the tuna completely and place in a mixing bowl. Flake with a fork. Add mayonnaise, lemon juice, white pepper, and chopped chives. Mix well and taste for seasoning.

Wet your hands with water and sprinkle with salt. Take a handful of rice (about ½ cup) and create a small well in the center. Add 1 teaspoon of tuna filling. Cover with more rice and gently form into a triangular shape, pressing firmly but gently.

Cut nori sheets into thirds lengthwise. Wrap the bottom portion of each rice ball with nori. Sprinkle the top with furikake seasoning. Serve immediately or wrap individually in plastic wrap.