Every country has a healthier version of its staples in the modern world. This is a recipe that you are unlikely to find in a standard Japanese cookbook.
The number "five" (go - 五) has a special significance in Japanese cooking. Traditional Japanese cuisine — washoku (和食) — has long been characterized by the principles of "five colors, five tastes, five ways, five senses, five outlooks".
It's really a shorthand for how to make meals more nutritious and serves as an organizing principle for daily meals. (It sounds hard but the CC assures you that it's shockingly easy in practice.)
The five grains mentioned obviously feature rice but there are other grains from the wheat family. They add both texture and nutrition.
The recipe below features -- white rice, brown rice, black rice, barley (mugi) and oats but in the modern day, you'll see everything from Job's tears (hato mugi) to farro to quinoa.
The general principles stand though. You want rice and you want a complementary set of grains for nutrition and texture.
The black rice turns everything purple and the dish is visually arresting. It also has a nutritionally complete set of amino acids and with the addition of the sesame provides a complete meal (even though that's not how it would be served.)
Lest this sound some like some "austere" dish from the land of peace, love and granola, the CC will tell you that you will be chowing this dish down faster than you can say "roast pork".
It's herushi (= healthy), it's visually appealing, it's delicious, it's nutritious, and it's addictive!
It's a modern-day classic of Japanese cooking.
1/2 cup white rice
1/4 cup brown rice
1/4 cup black rice
1/4 cup barley
1/4 cup rolled oats
2 1/2 cups dashi
1 tbsp sesame seeds
 The proportions are 2:1:1:1:1 with the white rice being 2. That adds up to 6 units so you want about 10 units of the dashi. You can always add more water later.
 The various soaking times are different because the stuff is cooked together. If you don't follow this, the softer stuff will be mush while the harder grains have barely softened.
 The sesame seeds act as a white counterpoint to the purple. They are also necessary for nutritional reasons. The fat is needed for the absorption of the amino acids. The CC also sometimes sprinkles gomashio (= sesame and salt roasted and powdered into a fine white powder.)
 The purpose of letting the dish to sit for a few minutes afterwards is that the starches bind the dish together. It makes it easier to eat with chopsticks. If you're not a chopsticks person, ignore this point. Also, this dish is made for bento boxes. It's awesome at room temperature.
 The dish is a game of texture. It's chewy and each bite is different because of all the various grains. This is one of the reasons it's "addictive".
Soak the black rice in a bowl for at least 4 hours.
Soak the brown rice in a bowl for at least 2 hours.
Soak the barley in a bowl for at least 2 hours.
Wash the white rice in copious water until it runs clear. Wash the oats too. Let them drain together in a colander. (This level of "soaking" is sufficient to get the right texture. You don't want them too soft.)
Drain the water from the other three components and mix together.
Combine the five grains, the dashi with some salt and bring it to a boil. Let it cook in an open pot till the liquid has been absorbed, roughly 10-12 minutes. Check that the grains are cooked. If not, add some water and let cook further. They should still have a chewy bite (= al dente).
Turn off the heat and let it sit for 4-5 minutes.
Meanwhile, lightly roast the sesame seeds in a skillet till they are golden. Set aside.
Sprinkle the rice with the sesame seeds and serve.