Gyudon is one of the most know Japanese food these days, and I only make Gyudon with fatty Japanese beef slices which I buy in Meijiya. Because this dish that has to be made with thinly sliced beef.
In Japan, meat is usually sold a package of thin slices. This is the biggest difference of the way of cooking the meat from western countries or Asia; Singapore or Hong Kong to Japan. Basically, Japanese people only cook sliced meat but hardly the block of meat.