Make the sauce:

1. Put the soy sauce, mirin, sake, and sugar in a small saucepan and stir to combine.
2. Bring to a simmer over medium high heat, stir once more and cook for 10-12 minutes until the sauce is reduced to a syrupy consistency.
3. You will yield about ⅓ cup of sauce. 

For the Unagi:

1. Preheat the oven with the broiler setting and move the oven shelf to the second from the top. 
2. Line a baking tray with aluminum. Spray lightly with oil. Cut the eel fillets in half lengthwise and then into 3 pieces to yield 6 pieces total. 
3. Place the eel on the tray skin side down. Broil the eel for 4-5 minutes and then brush with the sauce. 
4. Broil for 1 more minute.
5. Divide the rice into 3 large bowls. Drizzle a tablespoon of soy glaze over each rice bowl. Top with the eel and a little more sauce. 
6. Sprinkle the eel with the sansho powder and garnish with a little red ginger, if using, and serve immediately.