If I want stay in Tokyo for two days, what should I do?

It depends on your interests of course. There is a lot for nearly any taste.

For Tokyo, look through these sites:

http://www.gotokyo.org/en/index.html

http://www.jnto.go.jp/eng/location/regional/tokyo/index.html

http://www.ar.jal.com/world/en/guidetojapan/city_information/tyo/see/akasaka/

http://www.japan-guide.com/e/e2164.html

Within Tokyo, there are subway passes, such as on:

http://www.tokyometro.jp/en/ticket/value/travel/index.html#anc03

But for 2 days you'd need to ride a bit to recoup the costs. So maybe it's worth it or not; depends on how much you are exploring Tokyo. Another alternative in a JR Tokunai Pass for 750 yen per day, you can ride the JR Yamanote Line which goes to many popular tourist places.

Thank you very much!!!