[Hatredcopter]

You need:

1. A lot of money (at least to start out)
2. A 4-year bachelor's degree
3. Fluency in Japanese

#3 is only a requirement if you want to go to university in Japan. At Japanese universities, classes are taught in Japanese (duh), so you'd need to be completely fluently to attend one. You can't move to Japan without a four-year degree or without attending a university there/getting your degree there. The only other feasible way is to marry a Japanese national. There are a small number of universities in Japan that have English courses, but they are very expensive and there's limited majors to choose from.

I suggest attending college in the US (or wherever you're from) first, for two reasons.

1. You can learn Japanese, as larger universities in the US offer Japanese. You can also choose to study abroad for a semester or year in Japan, which leads me to...
2. If you enroll at a school in Japan and find you've made the wrong choice, you've wasted a lot of time and money. Attending a university in your home country and then taking a study abroad trip to Japan will allow you to live there long enough to see what daily life is like before making a life-changing decision to actually move there.

Hope that helps, if at all.