In a pot, combine soy sauce, mirin, sake, and kelp and bring to a boil over medium heat. Once boiling, reduce to a simmer then add the bonito flakes. Simmer on low for 3 to 5 minutes. Strain and cool in the fridge.
Scoop the rice into a bowl and shape it into a round dome shape. Set this aside for a few minutes to allow the rice to come to room temperature.
While the rice is cooling, slice the salmon into 1/4-inch thick pieces, preferably at an angle for better presentation.
Once the rice has cooled, add 1 teaspoon of the mentsuyu sauce from earlier over the rice.
Top the rice with sliced salmon, by arranging it around the dome. For better presentation, you can slightly overlap the salmon to cover the rice completely.
Top with sliced avocado, shiso leaf, fish roe, and wasabi,
Drizzle another teaspoon of the mentsuyu sauce over the salmon. Add more if needed.
Serve immediately!
Notes
1. Feel free to substitute the salmon for any other sashimi-grade fish such as tuna, amberjack, fluke, etc. 2. You can purchase bottled mentsuyu sauce at a Japanese market. 3. The homemade mentsuyu sauce will last in the fridge for up to 4 weeks!