Fast food is synonymous with unhealthy food, at least in the West. In Japan, it is not so bad. For example, the last place I dropped in for a quick bite, this is what my $9 got me:
Lightly fried fish, shrimp, squid, and vegetables in batter
a bowl of white rice
a bowl of miso soup
a small side of pickled vegetables
a cup of green tea at the beginning and a cup of brown tea at the end
The rice and miso soup have free refills.
OK, that is not quite right. That was about $6. I also ordered a glass for beer, which brought the total to $9.
And it is fast. Many places have a ticket machine outside where you purchase your meal. You take that in, sit at the bar, and hand it to the servers. A few minutes later you have your food. And when you finish, you just leave. Click on the image for a larger view.