If that's from the DMM Store .apk then you could try the QooApp Store .apk. QooApp only has the All Ages version of FKG, not the 18+ version. It at least doesn't require a VPN.
But I did download the game with QooApp, on both the phone and tablet. I think because I registered on the former device first a long while ago, the latter is unable to register for some reason. At least, that's the only explanation I'm working with.