: Using a modified APK on the same device as your official account is incredibly risky. Aniplex and Lasengle have strict anti-cheat/anti-tamper policies.
If your primary goal is to experiment with team compositions or simulate summons without the grind or risk, there is a much safer alternative: . Fan-made projects like "Grand Order Battle Simulator" (often found on GitHub) or other web-based tools allow you to create teams, equip Craft Essences, and simulate battles entirely offline or in a safe, isolated environment. This gives you the sandbox experience without any of the legal and security risks of connecting to a private server. fgo private server
Private servers, also known as "private servers" or "custom servers," are unofficial game servers that allow players to experience FGO in a more personalized environment. These servers are not affiliated with the official game developers, Aniplex or Delightworks, and offer features not available in the standard game. : Using a modified APK on the same