Kushi Katsu
Kushi Katsu is basically deep fried skewers of various meats, vegetables and seafood dipped into a sauce. There is a specific eating style that you should adhere to that involves never dipping into the sauce twice (hygine reasons). You can find plenty of guides online already on the etiquette.

A popular chain of Kushi Katsu is Kushi Katsu Tanaka, which can be found all over Japan. The location near Yoyogi station is quite nice and worth a visit. Originally a food from Osaka, there are obviously plenty of places around there. The food tends to all be roughly the same quality and it isn’t supposed to be high class, so pick a place with a nice atmosphere that serves cheap beer. Expect more business men after work than families out for dinner. A recommendation in Osaka is here (the area is also great for many other types of food).

Cheat sheet menu
Kushi Katsu Tanaka has a nice menu but without English, so “When Japan” added some English to help you out. Perhaps in the restaurants themselves there is an English menu. Other items will be available but the basics are below. If in doubt, the always useful “Mori-awase” (selection) can save you. Usually they will do a 5 or 10 skewer set for a fixed price. When you order always say how many sticks you want (they will ask if you don’t).
