Under "Country and profiles," you should see an option to switch to the Japan Play Store (this usually requires being on a Japanese IP via VPN).

Furthermore, the ethical and legal gray areas cannot be ignored. While downloading a free-to-play Japanese game via a VPN is generally tolerated, circumventing region locks to access cheaper in-app purchases or subscription services (a practice known as "region hopping") violates Google’s Terms of Service and can result in a permanent account ban. For developers, regional locking is often a deliberate choice, driven by licensing agreements (e.g., music rights in a rhythm game) or local data privacy laws. By forcing the Play Store to show the Japanese catalog, the user is overriding those developer intentions.