americans have the awesome benefit of not really being welcome many other places unless you have a 4year degree.
if you were canadian or australian or european you could come to Japan and get a job on a "working vacation" visa,
Also if you have your own multi-million dollar company and want to move here for business reasons, they are cool with that.
Your easiest option if none of the above apply to you is to visit here for up to 90days, learn as nuch japanese as you can, and find a girl.
If you find one that you would marry, then youre golden. you can work on a spouse visa almost indefinitely.