Where to get gyudon?
You will find the Japanese beef bowl served at a lot of Japanese styled restaurants (washokudo) but your best bet is to head over to one of Japan's gyudon chain restaurants. Sukiya, Yoshinoya and Matsuya are the three major beef bowl chains found all around Tokyo, as well as in other areas of Japan, and this type of "fast food" has been around for a long time - Yoshinoya was founded in 1899! In addition to classic gyudon, there are lots of variations and toppings, Japanese curry and sometimes noodles, hambagu, nabe (hot pot) and Japanese breakfast on the menus. Most restaurants are open 24/7 so you can always get a tasty bowl of guydon.
How to order and eat gyudon?
Some of the restaurants have vending machines near the entrance, where you order and pay (mostly at Matsuya). If you're lucky the vending machine is one of the newer ones, which means it has a touch screen and multilingual menus. After you have made your order and payed, you get a small receipt that you give to the staff who then prepares your food.
If there's no vending machine you simply take a seat at a table or the counter and the staff will soon greet you with water or tea and take your order. Some restaurants do have English menus, but at least they all have menus with pictures so if you're not that comfortable with Japanese you can always look at the pictures, choose and point to the staff.
The standard (normal) size is most often kalled nami 並. But depending on the chain you can also order a mini, a medium (larger than standard), big, extra big or mega. I usually go for the standard size with soup and that is enough if I'm not starving, otherwise I'll opt for one size above standard and end up feeling more than full.
Water and tea is usually served when you sit down, and you can always ask for more or refill yourself if there's a pitcher nearby. When you have gotten your food feel free to use some of the complimentary sauces, benishoga (Japanese red pickled ginger) and spices to adjust the flavor of your dish.
There are slight differences between the chains, but they all serve delicious and affordable meals. And did I mention that the food arrives within a few minutes after ordering?
Sukiya is the largest of the three big chains with over 2000 restaurants is all of the 47 Japanese prefectures. They serve beef and pork bowls, Japanese curry and also has some raw tuna dishes.
Yoshinoya is the oldest chain and also has locations in all 47 prefectures. They serve beef and pork bowls, as well as shogayaki (ginger pork). From time to time they serve vegetable packed "vege bowls" (with or without meat) and they also serve their famous black curry.
Matsuya calls their gydon gyumeshi, which literally means beef rice. They also serve Japanese curry, udon noodles and hambagu (Japanese style hamburger steak). At Matsuya the miso soup is included in the price which is great!
All of the chains also boast a variety of side dishes like different kind of miso soups, salads, pickles, kimchee, tofu and toppings such as cheese, soft boiled or raw egg, leek, seaweed and natto (fermented soy beans). Dessert and drinks are also available, including beer and whiskey highballs at some of the restaurants.
All of the chains serve seasonal items as well. In early spring I ate sukiyaki at Yoshinoya which was super tasty but a fraction of the price of what a sukiyaki normally costs. Right now they are serving taco rice and vege bowl with tomato sauce while Sukiya is serving unagi, freshwater eel, also at a very reasonable cost.
Since most of these restaurants are open all hours of the day they also serve breakfast items, from a separate breakfast menu, usually from somewhere between 4am to 11am depending on that specific restaurant. The breakfast sets always include rice and miso soup and you usually have a choice between beef, different fish dishes, ham or bacon. In smaller cities or remote areas of Tokyo some restaurants may not be open 24/7 but will still have decent opening hours. All three of the big beef bowl chains also offer special kids menus complete with soft drinks and dessert.
The number and variety of dishes is also quite large, making this a safe bet for most people.
It might not be the best choice if you don't eat food containing meat, since even the curries and udon contain beef or pork, although Sukiya have tuna dishes if you eat fish but not meat. I don't think there are any options on the regular menus for vegetarians or vegans, but keep an eye out for those seasonal vege bowls. In addition to these tree big beef bowl chains there are lots of smaller places also serving up the cheap and delicious gyudon all around Tokyo and Japan.