The taxonomy is confused. Generally, the American raspberry (and that would include any everbearing forms) is considered as a separate species, Rubus strigosus, although many classify it as a subspecies of the Eurasian raspberry, Rubus idaeus. If you accept that concept then the American berry is Rubus idaeus subsp. strigosus and the Eurasian is Rubus idaeus subsp. idaeus.

Whether or not these plants grow wild in Japan currently is not something I can speak to but they apparently have been known to grow in that area at some point in the past.

Ok so other than strigosus, there should be no reason that rubus idaeus be considered American native. And what do you mean by grow in that area, like As in cultivated for fruit production or naturalized? And you are talking about the subsp. idaeus right? There are so many subspecies of this species in Japan but wondering about subsp. idaeus.

Also do you know if the raspberry plants that are typically sold in nurseries a subsp. idaeus?

Most raspberries sold in nurseries would be hybrids of the two sub species. No idaeus in Japan afaik, rubus sachalinensis is the Asian subspecies.

I've decided to try growing rubus phoenicolasius instead. Heard their raspberries are much sweeter than rubus idaeus

I guess it depends on the climate but to me the wineberries were very bland in comparison, quite disappointing really. I found Polka raspberry the sweetest, followed by wild rubus idaeus. Boysenberries are also very sweet.