Thanks for your advices
As I said, the problem with Wwoofing is that I have to register on their website and I'm not sure to find a place to stay (I would like to stay near Tokyo and there are a few persons in here
So does somebody know the same kind of association ?
Working Holliday is interesting but the problem is that... I don't speak japanese so it will be a little bit difficult for me to find a normal job
By the way, thank you again for your answer Firebird.
@Teresa, why guts ?