There is no condition to join a Guild.
When you clear the tutorial, you can join any Guild you want.
■ Joining a Guild
① Tap the 'Menu' icon (=).
② Tap on 'Guild'.
③ Tap on 'Join Guild'.
④ Shows recommended Guilds.
⑤ Use the 'Search Guild' to search for a private or specific Guild.
⑥ Tap on 'Register' if you find the Guild you want to join.
⑦ Tap on 'Yes'.
⑧ You can check the joined Guild and proceed with Guild activity.
※ The guide was produced in a separate test environment.
So, It may change depending on the update and development situation.
Thank you for your love and interest in the Devil Book~
Devil Book Team