You can get a small-sized cup of coffee for free in McDonald's until October 18 in Japan. But the campaign hour is from 2 pm to 9 pm. Moreover you can not get a free cup of coffee if you purchase a set menu.
When I went to McDonald's today, I only got a small-sized cup of coffee for free as shown in the picture. The store was very crowded that day because of the campaign.
If you are traveling in Japan, it is a good chance for you to get free coffee until October 18.