The air levels are normal. I was more concerned about the possibility of tainted water/food. Once I step foot in Japan, I was fine and able to enjoy my trip. I ate and drank as normal.

As for things to do- aside from people watching/shopping, a lot of the sightseeing revolves around shrines/temples. IMHO, they all start to look the same after 2 or 3.

Here's the sightseeing I did in Tokyo:
1. Asakusa- Sensoji Temple & Nakamise Shopping area- arrived around 3:30 pm and went straight to the temple to take pictures before sunset. The pagoda and temple are lit up at night, so we walked around the shops, then went back to take more pictures with the lights.

2. Tsukiji Fish Market- got there around 11 am, which was too late to see the fish. I think you'll see more before 9 am. Had lunch at one of the small restaurants in the outer market.

3. Imperial Palace- Walked around the East Gardens and took pictures of the fall leaves. It probably won't look very nice in January once most of the leaves are gone. You can't go into the palace or even see much of the outside.