Wash 2 cups of Japanese rice and drain it very well. Then, put the washed rice into an instant pot and pour 2 cups of water. Next, close the lid and vent. Push the manual button, adjust time to 6 minutes at high pressure and naturally release pressure.
While waiting for the rice, slice a medium sized onion.
After that, cut 2 sticks of green onion.
Pour ½ tablespoon of vegetable oil into a non-stick pan and add sliced onion. Stir fry them a little bit, then add 4 tablespoons of soy sauce, 4 tablespoons of mirin, 2 tablespoons of brown sugar and ½ cup of water. Let it simmer for a couple minutes until the onion is a little soft. Next, add thinly sliced beef into the sauce. Let it simmer for a minute or two until it changes color.
After that, turn off the fire and add ½ tablespoon of sesame oil, green onion and mix them well. When rice is done, scoop the beef with sauce over the rice.