Generally, the router works better in cities. Don't know any reasons, it will be disconnected suddenly, especially in rural areas or forests. The big problem is : as visitors, we cannot return the router to any convenience stores or post offices as we don't have any address in Japan as stated. We have spent some time in communicating with the staff both at convenience store (Family Mart) & post office near Fukuoka Airport. It has wasted us around 20 minutes and caused us some delays in flight check-in.