1. Wash the rice two to three times in a sieve with cold water until the water runs clear. Then drain for about 15 minutes.
2. Cook the rice in a rice cooker or cook the drained rice in a large pan with 650 ml of water. If using the saucepan, make sure the rice comes to a boil. Then turn the heat low and place the lid on the pan. let it cook gently until the rice has absorbed all the water. Finally, let the rice cook for another 15 minutes with the lid closed.
3. Ladle the warm, cooked rice into a spacious bowl made of unpainted wood or pottery. Next, add sushi vinegar.
4. Season the rice well with the sushi vinegar and stir gently with a wooden spatula. While doing so, try not to bruise the rice grain. Quickly cool the rice under a clean wet tea towel and let it stand for 5-10 minutes.
5. Using a very sharp knife, cut the fish into thin 10g rectangular slices, about 0.5cm thick, 5cm long and 2.5cm wide.
6. With a clean, damp hand, take a little rice from the pan and knead it into a rectangular shape. Remember that this is a one-person dish, so don't make the nigiri too big.
7. Place the different types of fish on top of the rice balls.