Hey good suggestion I am actually staying in Mercure Ginza.
Since you@Ginza and are busy, here are some things to do at Ginza that are unique to the area. All of which can be seen or done quickly.
1) Ginza has lots of omise. While this means "shop", it also means an old, long-established shop. Meaning in business for > 50, some > 100 years; specializing in only one thing.
The Japanese appreciate this level of singular dedication. I like gyoza (Tenryu) and tempura (Tenichi) - very very good. Even something simple like fried chicken (karage) has an omise for it.
2) Ginza has a very unique toy store called Hakuhinkan on the western end. Something like 7 floors of toys, some of which can only be found in Japan.
3) At the center of Ginza, look for a building called Wako. It's an old style Ginza department store. Famous for being, at one time, the highest priced real-estate in all of the world.
4) The Ginza Kabuki theater. This was recently re-opened after going through renovations for 2 years. You cannot miss it - it has huge sake barrels in front of it. The great thing getting an intro into Kabuki is that they sell tickets to short acts e.g. you can buy a ticket for 15 minutes of Kabuki. A Kabuki play is half-a-day in length made up of many acts. You can go in and out and get just see a short act.
On your way back to airport, if you are taking the Ne'x train, stop and linger at Tokyo station for a while to a) see how busy and complicated it is b) it was recently remodeled with a new 6-star hotel nice inner court views. If you have time, the imperial palace is a short walk away from Tokyo station. As you walk there, you will pass by the Otemachi distruct - this is the financial center of Tokyo. You won't be able to go into the palace though (it's only opened during New Year's) but you can see the walls, moat and more importantly, the gates.
When you go back to Narita on the Ne'x, you pass by some rivers - they used to define Tokyo life back when it was Edo but today, nondescript - Edogawa (gawa means river) - lots of historical stories and plays written about it. Once you cross over Edogawa you are in the Chiba prefecture - that's where the airport is. If you really have time, you should stop at the Narita station which is the stop before the airport. This is Narita town and there's a famous temple (Narita-san) you can walk through to from the JR station through Narita old town. Narita town is famous for its unagi (eel). Also lots of rice farms when you get close to Narita - you will understand why Narita cannot expand, why there's a ticket check before you enter the airport and why Narita airport has a curfew - it is not 24 hours. The farmers in the 70s protested the creation of Narita and the expansion of Narita and made many threats. Rice farmers are politically powerful in Japan.
