Cook the rice with 2 cups of water. Bring it to a boil and turn to low heat for 20 minutes. Turn off the heat and let it rest for another 10 minutes. Remember to put the lid on while cooking and resting.
Cut the beef and the onion into thine slices.
Heat up a pen and fry the beef with low heat until its cooked. Remove the beef from the pen.
Combine soysauce, mirin, rice wine and dashi. Cook the mixture in the same pen until it boils.
Add onion and grated ginger in the boiling mixture. Cook for 3 minutes.
Add the cooked beef into the pen, cook for another 3 minutes.
Serve the beef with sauce on top of the rice. You can add some green onion if you like. Enjoy!