Not all Japanese food has seafood in it, it's just natural that it permeates their dishes since they're an island nation. There are a lot of entées you can easily find such as: donburi (a variety of which use meat), soba and zaru soba, udon, tenpura usually has shrimp or squid, but it doesn't have a very seafood-like taste, niku jaga, curry, ramen, etc.
You'll have a hard time finding lamb, though ☝ I don't think you'll have any trouble finding things to eat, if all else fails the conbini has a large selection of foods. There are also a lot of Western chains, as well as nihon-fuu western chains like mos burger, first kitchen, and lotteria. The general quality of the ingredients used in Japanese food are more fresh and of higher quality, which translates into better food (I'd avoid McDonalds though, they suck no matter where you go). Real Japanese seafood is also quite good, I'd recommend trying everything to see what you like. Maguro (tuna), Unagi (eel, mmm), Ika (squid), Hamachi (yellowtail), Hotate (scallops), and Tako (octopus) are all very well integrated into japanese cuisine, I suggest giving them a shot!
edit// also, I recall there being a completely western-style supermarket run by kinokuniya where everything was actually imported from the states; might be a bit hard to find though, and likely more expensive than your typical supermarket.