This app was mentioned in 3 comments, with an average of 2.67 upvotes
iOS: https://itunes.apple.com/jp/app/final-fantasy-brave-exvius/id940099765?l=en&mt=8
Android: https://play.google.com/store/apps/details?id=com.square_enix.ffbejpn
https://play.google.com/store/apps/details?id=com.square_enix.ffbejpn&hl=en
https://www.reddit.com/r/FFBraveExvius/wiki/starting-guide/rolling-and-rerolling
https://play.google.com/store/apps/details?id=com.square_enix.ffbejpn
https://apkpure.com/final-fantasy-brave-exvius/com.square_enix.ffbejpn