This does mean that Stripe users in Japan can charge in USD, or our other supported currencies. You put the currency in the API call based on whatever logic you want; we charge the user's CC in the specified currency; we credit your bank account JPY at the appropriate rate. (I work at Stripe, in Japan.)

As is typical for Stripe, this involved an ungodly amount of offline work to enable an extra query parameter that most of our customers will never have to think deeply about the implementation of.