This app was mentioned in 6 comments, with an average of 1.67 upvotes
https://play.google.com/store/apps/details?id=com.aniplex.koyomimonogatari
If it still wont' let you install, there is still a region lock on the app itself. In that case there are a few ways to bypass it. Either by having your Google Playstore Account set to Japan, or by downloading the apk from somewhere.
this one. you need a japanese google play account to download it tho