Expeditions
Expeditions provide another method to earn some extra items and gain experience. Assign a character to lead the expedition, then wait for it to complete. Characters sent on expeditions will not leave the party. You can send them on expeditions and still use them in combat. You will easily earn extra items and enough experience to give a one-star character a full level each time. Even characters that have gone through "Rebirth" can still earn experience through expeditions.