Almost no chance I’m afraid. This is the absolute peak tourist season in Japan at a period when it’s profile as a tourist destination has never been higher. I doubt there will have been more than the minimum 2J 4Y tickets released for Avios. There is always a chance that seats can be released last minute if loads are low but this tends to be business focused routes where demand/loads can fluctuate as plans change. The vast majority of passengers on these flights will be tourists so chance of changes to travel plans are far lower.