Wash the rice 3 to 4 times until water is clear. Drain rice thoroughly, add to pot, and cover with all liquid ingredients. Let liquid soak into rice for 20 minutes to 1 hour. Add shimeji mushrooms to the pot, place over medium-high heat, and stir occasionally until liquid comes to a simmer. Cover pot, lower heat, and cook for 16 minutes.
While the rice cooks, prepare remaining ingredients and arrange on a plate.
When the rice is ready, fluff the rice, stirring from the bottom; cover again and wait five minutes. Serve with aromatic garnishes to taste.