Originally Posted by JALPak

My understanding is you can reserve the J-class seats in advance when you buy a standalone domestic ticket from JAL or you are on an international business class ticket connecting on a JAL domestic. Other than that, you will have to do it at check-in time. But I could be wrong, you can check with JAL or post the question on JAL forum to verify There are probably more knowledgeable FTers on this topic on the JAL forum as I mostly fly on JAL international flights.