EP and AP are the main resources you need to start different types of missions. EP is used for special event missions and AP is used for the other areas such as story missions or SP missions.

After consuming them entirely, each of them will recover over time to a maximum number determined by your level. You can speed up the process by using energy items. Each type of energy has its corresponding items and those can be acquired through daily missions, random drops, completing achievements, Lucky Wheel spins, or by purchasing them from the shop.