Let's face it. Almost everything "American" (or otherwise foreign) in Japan is modified to suit local tastes. This is true in America, of course - sushi, tacos, and kung pao chicken are all Americanized in the States.
I haven't hopped back across the pond since arriving in Japan three years ago. I've managed to satiate my homesickness and cravings for American food by finding alternates or paying the price for imported goods. But sometimes you just gotta feel like you're back in America.
When it comes to an American menu, I think Toy Box just about does it as authentically as possible. The menu is truly American, full of nachos and burgers and tacos and even big banana splits! Okay, they slipped taco rice in there too.
And the decor is retro kitsch:
The staff is really nice and I think they understand a good bit of English, which certainly helps! It may be off the beaten path for most, but it's still relatively accessible and a better place to get dinner after a day at nearby Koshigaya LakeTown shopping mall.