Here you go! Right now commercial VPNs do not work, you have to use VPN Gate and an individual server, and may have to try a few until you find one that works.
The VPN in the pinned guide is free and works for Rakuten! You just need to use the VPN when you're making an account, doing the purchase, and until the video loads and then you can turn it off and the video will still play. I've also recently tried ProtonVPN since one of their free locations is Japan, although not for Rakuten specifically, and it worked great for a different website!