Original Reddit Thread: https://www.reddit.com/r/grandorder/comments/hfbz0h/fgo_save_files_for_na_and_jp_play_on_multiple/
Disclaimer/Notes: Created as of 2020.09.08. In case DW or Aniplex decides to change the file save structure, this should work. I can confirm this from my own end, playing off my Main Account between a Samsung Galaxy S10e and the Samsung Galaxy Tab S5e. I've slightly modified the steps for more clarity using a file explorer agnostic of Operating System. This also personally for me in preparation for Gilfest 2020 and potential usage with the Fate-Grand-Automata autorunner for less pain in farming lotto.
Majority of credit to /u/vanwayne8 on Reddit. A small guide for copying save data of your Fate/Grand Order account so you can play it in multiple Android devices and emulators without losing your transfer code o