JAL should announced around December 1st the fuel surcharge that will apply for tickets issued from January 1st to March 30th. I expect them to be far lower than the actual one's, as it will be calculated with the average price of oil from August 1st to October 31 (the actual surcharge is for a oil range price of 140-150$).
So if I were you I would wait January 1st to book.
Tickets for the second half of January to April should be the cheaper, except for the school holidays period. Early May tickets will be very expensive because of the golden week. After that you can aim until the end of May. Starting June, prices are getting up again.
Just my personal view and experience.

Regards,