The Japanese food most Americans are exposed to is made for a restaurant or grocery store. When you come to Ikata, you will be eating day-to-day, home-style Japanese food.
Japanese cuisine puts a big emphasis on whole (minimally processed) foods, and salty or pickled food. Rice or plain bread is the base of every meal, surrounded by a number of small side dishes providing protein, fiber, iron, fat, and roughage.
Ikata has access to a lot of seafood and seaweed. Some things you may not be expecting are chirimen, tiny white sardines that are dried or fried and eaten whole; jakoten, palm-sized patties of ground whole fish; and hijiki, a kind of seaweed that looks a little like a black coleslaw, boiled with mirin and sugar. In addition, there are some varieties of glutinous potato which feature as a side salad or in okonomiyaki. You may have heard of natto, fermented , viscous soy beans eaten with soy sauce and raw egg or spread on toast. Eggs are not always refrigerated, and are mixed with soy sauce and eaten raw with sashimi (raw fish) or with shredded daikon (giant radish) on top of rice. These are all typical foods, nutritious and delicious.
Your host family will probably not give you natto or sashimi without asking you how you feel about it. They may give you Western style food if they feel you are not eating enough. The US, though, is not the only country that has contributed to Japan's image of "Western food." France has had a big influence. So don't expect all the bread, soup, stew, pizza, gratin, etc. to taste the same, but do keep your tastebuds open to delicious new flavors!
Most of the milk sold in Japan is whole, not low- or non-fat, and the taste is slightly different from American milk. Cheese is very mild. Breakfast cereal is still a rarity, and there are often only a few kinds to choose from. Most people eat a Japanese style breakfast of rice, miso soup, and fish, or a Western style breakfast of various sweetbreads, or eggs and sausage. "Scrambled" eggs are made like an omelet and folded over into a neat patty, and may contain sugar. Pancakes ("hot cakes") and waffles are considered desserts and not breakfast.
Last word: try everything and be polite, but don't push your body past its natural limits.