I found the following, at time of writing it is still functional and working.
Alitali offers a discount of 25K Yen on its Japansese site. Booking a tickets AMS-FCO-AMS for example is less then 25K so it's basicly free.
Go to the Alitalia website and select the Japanese site, use Google chrome to translate (for you easy)
Just book whatever you want and make use of discount coupon PROMOJP and make sure it recalculates. If your total price is under 25K Yen you will not be charged.
Ofcourse I can not guarantee Alitalia will drop your booking afterwards, I have however, received my eticket with valid number and PNR.
Good luck! Curious what you will book!