https://www.techdirt.com/articles/20180720/06192740272/eu-japan-agree-to-free-data-flows-just-as-tottering-privacy-shield-framework-threatens-transatlantic-transfers.shtml

The EU's strong data protection laws affect not only how personal data is handled within the European Union, but also where it can flow to. Under the GDPR, just as was the case with the preceding EU data protection directive, the personal data of EU citizens can only be sent to countries whose privacy laws meet the standard of "essential equivalence". That is, there may be differences in detail, but the overall effect has to be similar to the GDPR, something established as part of what is called an "adequacy decision". Just such an adequacy ruling by the European Commission has been agreed in favor of Japan:

This mutual adequacy arrangement will create the world's largest area of safe transfers of data based on a high level of protection for personal data. Europeans will benefit from strong protection of their personal data in line with EU privacy standards when their data is transferred to Japan. This arrangement will also complement the EU-Japan Economic Partnership Agreement, European companies will benefit from uninhibited flow of data with this key commercial partner, as well as from privileged access to the 127 million Japanese consumers. With this agreement, the EU and Japan affirm that, in the digital era, promoting high privacy standards and facilitating international trade go hand in hand. Under the GDPR, an adequacy decision is the most straightforward way to ensure secure and stable data flows.