Announcement reposted from Amazon Japan:
Amazon has launched the Buy More & Save program. If a customer buys four or more promotion-eligible items, Amazon will fund a 5% discount from the total amount of promotion-eligible items at checkout. This does not impact the price at which FBA sellers sell their product because Amazon is funding the Buy More & Save discount. This will not affect the payment amount to FBA sellers.
For more information go to Buy More & Save.