In the fall, many universities throughout Japan have big festivals called 大学祭 daigaku-sai, meaning university festival, or 文化祭 bunnkasai, Culture Festival. They are basically street fairs held on campus, with lots of food and fun stalls, concerts, even ghost houses and amusement rides. Many of the big ones also hold concerts in which top Japanese singers and bands appear. Daigaku Imo, which means University Potato, are candies sweet potatoes, a sweet and slightly savory snack that is often served at university festivals in Tokyo.
The snack itself probably originated as a cheap, calorie-rich, affordable snack sold to cash-poor students around universities in Tokyo around the turn of the 20th century. The idea for deep frying and then sugar coating potatoes most likely came from similar snacks in Chinese cuisine.
Daigaku imo is simple to make, yet a bit tricky. You ideally want to coat the sweet potato slices completely with a hard caramel sugar coating, but too often the sugar gets crystallized. It doesn't taste bad when it does, but it looks far better with a shiny, smooth coating. I've found the best way to accomplish this is to make a fresh batch of the sugar coating for each batch of potatoes cooked. This is not diet food by any means, but regardless, to me they are one of the main treats of fall.