Basically, Raid Battle is a special feature where a mission must be completed. The game mode enables you to find exclusive materials for exclusive spheres and items in Randall
Here's what it looks like basically once you proceed with the quest. The Map will depend on the quest you'll take.
The mechanics are simple, you only have 30 minutes of time during every raid battle which starts counting down immediately after the room master starts the quest. You need to complete the mission before the time limit is up. You can also click the Quest Menu button (Found on the bottom right corner of the screen) in order to know your goal.
If your party lose all their lives, the mission will fail. If you give up the mission, it also counts as mission failed. Failure to complete the mission will forfeit any times that the boss might have dropped.
If you want to know more about Raid Battle, you can visit our article here.
Note: The Raid Battle unlocks when you reach level 40.