When you're in Tokyo Station and don't need to rush to catch a train, cruise through the new row of sit-down restaurants called GranRoof.
There's tonkatsu, sushi, izakaya food, nikuman, Italian and a few other options. My favorite is a tempura place about midway down the row. Their small and large tendon combos (tempura on top of rice bowls) are works of fried food art. A chef that you can watch from the bar fries the vegetables, seafood and egg yolks only after you order them.
Despite the GranRoof name, it's actually underground. Exit Tokyo Station from the basement level Yaesu central exit, then continue straight toward Daimaru department store and turn right into GranRoof across from Daimaru's depachika.