You accidently stepped right into an old inside forum joke.

Welcome to the Japan Forum - and Flyer Talk.

Without knowing your interests or demographic, it is difficult to suggest things to do. Assuming you are relatively mobile, on your own and have never been to Tokyo before, a few places come to mind. I'd recommend obtaining a Suica prepaid train/subway card to get around. If your 36 hours includes a trip to or from Narita Airport for arrival or departure, you can get a Suica+N'Ex card that includes the Narita Express airport train. If you are using Haneda airport, you don't need the N'Ex.

Is your 36 hours on your own at the beginning of your trip or at the end? How are you meeting up with your relatives? Will they get you to or from the airport? Will you stay with them or in a hotel? Lots of questions that impact advice we might give.

I'd suggest a visit to Asakusa Jinja (Senso-ji) Shrine in the older neighborhood of Asakusa; a visit to the Imperial Palace East Garden and palace viewing area; a visit to either Akihabara or Shikjuku for a look at the modern, fast-paced Tokyo and, if you want to see some really high-end shopping, a visit to Ginza. The Edo-Tokyo Museum next to the sumo arena in Ryogoku is very good, as are the national museums in and around Ueno Park in Ueno. Beyond that, your interests and desires come into play. Are you into nightlife or quiet, cultural places?

Others have ideas, too. Advice from me tends to be for tame, quiet places of cultural, artistic or historical interest (I'm kind of old and a bit dull.) For drinking and carousing, we have several regulars who can fill that bill.