Yokohama (Tokyo)
It's worth noting that most ships do not dock in Tokyo proper, but in Yokohama, a separate city around 20 miles southwest from Tokyo.
Though few cruisers will be visiting Japan to see Yokohama, this venerable port city has a number of attractions in its own right, most of which are a short stroll from where your ship is docked.
Many of the red-brick waterfront warehouses have been converted into attractions, such as museums, restaurants and bars, and make for an interesting walk if you haven't built in time to visit Tokyo itself.
Even if you've spent lots of time in other big cities, there is no way to adequately prepare for Tokyo. The sprawling modern metropolis is a dizzying kaleidoscope of flashing neon lights, pachinko (gaming) parlors, karaoke joints, standing sushi restaurants, robot hotels, maid cafes, tiny bars and basement noodle restaurants dotting its busy streets.
But quiet spots do exist throughout the city. Shinto shrines and Buddhist temples are great spots to stop and think about all you've seen, and there are a number of city center parks where you can find a secluded area. But don't wonder too far afield -- you'll likely hit a high-end and name-brand shop before you see the next peaceful oasis.
The Japanese take shopping very seriously, dedicating entire districts to it, like high-end Ginza or electronic-centric Akihabara. And their malls aren't just places to buy things; you'll find some of the best restaurants there, like Skytree Town at the foot of the 2,080-foot Skytree Tower -- as well as an aquarium and planetarium.
The good thing is that Tokyo is an amazingly easy city to get around. The massive metro and train system covers nearly every inch of the city, and though few people speak English, they will do their best to help if you just ask.