Do you have a college degree? If you don't, are you planning on getting one?
To teach there, legally, you'll need one to be admitted in the teaching system.
There are so many threads about this on this forum, all you have to do is a search for "teaching in Japan" and that will give you many threads.
I do find this thread very interesting and full of insight....
http://www.japanforum.com/forum/livi...ghlight=degree
I recommend you read it....