Although McDonald's, KFC, Burger King and other fast food chains exist in Japan, there are Japanese fast food chains too.
However, not like the customers order at the cashier and take their ordered meals to the vacant seats, customers sit first and the staff will come to take the order for the Japanese fast food. Therefore mostly the customers sit along the counters.
Beef bowl is the one of the popular fast foods in Japan, and there are several nation wide chains. Beef bowl contains beef and onions stewed in sweet soy sauce stock and put on the bowl of steamed rice. Of course you can choose the size. Normal, large and extra large but large usually does not mean more beef than the normal size. Large beef bowl has more rice than the normal size but the same portion of beef. On the other hand, extra large will have more portion of beef and rice than the normal size.
Nation wide chains are Yoshinoya, Matsuya, Sukiya and Nakau and beef bowl is called GYUDON in Japanese. GYU is beef and DON means bowl.