The most visible influence is American fast food. McDonald's and KFC are very common, and other chains such as Burger King and Wendy's are there too. There are also local versions - Japanese American-style fast food chains such as Lotteria and MOS Burger. Hamburgers, pizza, and KFC-style chicken - American cuisine's gift to Japan!

Less visible, but featured even more often on the Japanese table, is bread. Bread has a long history in Japan, with European bread arriving in the 16th century. The Meiji Restoration and modernisation/industrialisation brought bread back into the picture again, with Japanese breads such as filled buns appearing alongside European-style breads such as baguettes. However, it was post-war hunger that made bread a vital part of the diet. Japan came to the end of WW2 in a state of starvation - US emergency food aid saved many Japanese lives, and much of that food aid was in the form of wheat. Some of that wheat became noodles and gyoza skins, and much of it became bread. With post-war starvation long over, how common is bread now? About 50% of Japanese people have bread for breakfast, younger people more often, older people less often (Ashkenazi, 2000). Bread provides a quick breakfast, it feels modern, and goes well with coffee in the morning (or toast with milk for the younger breakfasters).

Breakfast cereal - another American influence - is also common. The milk could also be considered influenced by American food, as the post-war US food aid was also milk-prominent, and helped drive the growth of dairy consumption.

More broadly, there has been a lot of Western influence on Japanese food from the late 19th century onwards. The influences above are the ones that appear to be most specifically American, rather than simply Western.

Bibliography:

Ashkenazi, Michael, et al. The Essence of Japanese Cuisine: An Essay on Food and Culture, Routledge, 2000.

Cwiertka, Katarzyna J. Modern Japanese Cuisine: Food, Power and National Identity, Reaktion, 2006.

Vaclav Smil, Kazuhiko Kobayashi. Japan's Dietary Transition and Its Impacts, MIT Press, 2012.