Difference between French bread and Japanese bread
One of the best known (if not the best known) breads in Japan is, in fact, very much like a brioche. Japanese Milk Bread contains butter and egg, it also contains a fair amount of sugar. The Japanese think of bread more like a sweet than a staple. Another sweet bread known in Japan is Maple Bread, it's even sweeter and really does taste like maple syrup.

If you are looking for something more like a French Baguette, Catija's advice in comments is excellent. The Japanese aren't big into sandwiches. The Vietnamese, however, have a huge French influence (whether they want it or not). The bread traditionally used for Banh Mi is a short baguette. If you ask for Banh Mi in Tokyo, someone will know just what you mean.