Tamago are eggs and they are very popular in Japan. In fact Japan consumes more eggs per capita than any country in the world other than Israel.
In sushi shops you can get eggs draped over rice as a closing course for a meal. Chirashi-zushi consists of fine layers of omelet sliced into shreds and scattered over bits of fish and vegetables over bowls of vinegared rice.
In sukiayaki raw egg is used as a dip for slices of cooked meat. On Japanese farms raw eggs are served cold, whisked and poured over rice that is barely warm.
Oyako-donburi has a soft-scrambled mix of seasoned egg and chunks of chicken poured over rice. Tamago-dofu is a delicate, semi-hard paste like tofu. Quail eggs are used as toppings for soba noodles, and hardboiled eggs are served with octopus, daikon and other items in stewpots of late-night oden street stalls.