There are currently 6 different regular backgrounds in game, each of them having three different versions. They are displayed when you play a Live. The last background is the random option, letting the game choose a background for you.
Background 1 - Classroom
Background 2 - Gymnasium
Unlocked at player rank 5.
Background 3 - Bridge
Unlocked at player rank 10.
Background 4 - Indoors
Unlocked at player rank 20.
Background 5 - Open Air
Unlocked at player rank 30.
Background 6 - Dome
Unlocked at player rank 40.
Event Backgrounds