Practice Missions
From A3! Wiki
Practice Lessons are the primary way to gain experience to rank up in the game. The first four plays are unlocked as you rank up, and subsequent plays are made available during/after events. There are five practice sessions for each play, one for each member of the troupe.
Clearing all the Practice Missions for the first time will earn you Dia.
Actor's High is achieved when the Tension bar (orange music notes) has filled up. Your Tension will rise by 4% each time a member from the same troupe as your practice partner appears in a session.