Marinate 300g chopped salmon (into square chunks) with 2 tsp udon/soba sauce and 1 tsp mirin. Mix well with your hands and set aside or refrigerate for 20 to 30 minutes.
In a saucepan over low heat, make a sushi vinegar by adding 2 tbsp rice vinegar, 1 tbsp brown sugar and 1/2 tsp salt. Stir until all everything is dissolved and you get a sushi vinegar solution. Set aside.
Cook 1 rice cup of Japanese rice in a rice cooker. Slowly drizzle the sushi vinegar into the cooked rice and use a spatula to stir and fold the rice lightly to mix the sushi vinegar into the rice.