Discover has an alliance with JCB, the #1 credit card of Japan. https://www.jcbusa.com/adding-jcb-card-acceptance/

And the reverse: https://www.discover.com/credit-cards/international-use/

Discover (mostly) works on JCB, and JCB (mostly) works on Discover terminals in USA.

This means that Discover is a 'guest' on Japan's credit card network. It's JCB that will have the main say of what is or isn't allowed in Japanese payments.

That's why I'm pretty sure Discover can't fuck around. They literally aren't powerful enough. JCB is the credit card power in Japan who is stronger than Discover. Even if they have Capitol One backing Discover now (and Diners Club International... And Pulse), Discover is too small to bully.

But the alliance system (JCB allowing Discover cards to work on most JCB terminals in the country) naturally allows Discover to still be used in the vast majority of Japanese transactions.

Discover has enough 'alliances' to be a card worth using. But also isn't big enough to bully like Mastercard or Visa. Maybe that changes in the future but today I think Discover is our best move at a reasonable alternative.