Japan has lots of IC cards in various regions, and they have spent a lot of effort integrating their system. Unfortunately some IC cards like Kumamon decided to

Japan has lots of IC cards in various regions, and they have spent a lot of effort integrating their system. Unfortunately some IC cards like Kumamon decided to opt-out due to high maintenance fees. AFAIK, you can go through up to 4 different company networks once you enter paid-area. Beyond that, you'll need to do the override settlement (乗り越し精算) with the help of station staff. https://en.wikipedia.org/wiki/Nationwide_Mutual_Usage_Service https://en.wikipedia.org/wiki/Nationwide_Mutual_Usage_Servic...