I believe the Libby lending feature on Kindle was limited to the US due to an exclusive agreement or something similar.
Kobo's OverDrive feature is different, but it's still region restricted and isn't available in Japan to begin with. However, since my Kobo Sage was once set to the US region, the OverDrive feature has been unlocked, and it looks like I can use it in Tokyo without any issues (though I can't test it anyway, as my local e-library doesn't use OverDrive).
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