I also cannot find Champions of the Continent in Google Play Store.
I think it's exclusive to Japan.
If you on outside japan, you can't find it in Playstore, even if you found it you can't install it.
I would recommend to download from taptap: https://www.taptap.io/app/160881
And here is playstore url if you curious: https://play.google.com/store/apps/details?id=com.square_enix.android_googleplay.octopathj
Where is the Japanese Google Play Store / Apple App Store?
That's the last url that i sent you was playstore url
What do you think?