Originally Posted by abmj-jr
You might get more specific help by posting in the Travel Destinations -> Tokyo forum of this site.
Do you have accommodations and such? I'm not sure what the rules are regarding unaccompanied minors in Japan, but there may be problems with hotels. The "legal" age is 20.
You will need a passport, but no visa is required to visit for 3 weeks as a tourist. Take lots of money as things are more expensive than you think. You can get yen from an international ATM, but make sure your card and any credit cards are "unlocked" for international use. Just call the 800 number before you go.
JR
Also, don't forget to have your "back story" ready if the immigration or customs guy/gal asks you why a 16-year old is coming to Japan by himself. Do you know anybody in Japan? Have that info ready, in case you need it. Otherwise, find somebody you "know" in Japan before you go.
You may take note of
tokyotraveler's
excellent adventure. I'm not suggesting that will be you, but (a) lots of good info there, and (b) a cautionary note for the unprepared.
Lastly, do visit the Tokyo forum in FT. It is more about all of Japan, and you'll learn very important facts, like how a SL600 V12 AMG with black tinted windows, 19" wheels, antennas from the back, an Inagawa "super tiger" sticker in the back, and low number license plates will never be stopped by the police when speeding.