What do I need for one year stay in Japan?
 

I plan on going for one year but I haven't traveled anywhere outside of the U.S. What papers do I need to be able to stay in Japan for one year?

There appears to be a lot of information here:
MOFA: Visa

You will definitely need a visa to stay longer than three months.

If you are planning to work, then you'll have to get a Work Visa.

If you are not planning to get a job, then I think you can get a General Visa for "Cultural Activities"

That link I gave you tells you pretty much everything you need to know about obtaining a Visa.

A job with a working visa or go to school with a student visa. You can only stay for three months on a tourist visa. But you can leave and come right back to get another tourist visa. But I would definitely say a job would be nice to have, this place is like chotto takai yo.

and when entering you have to prove that you have a flight to go back home within the time your visa is going to be valid (usually within the next year)