Easy gold, RSP, and experience
While in Elvi lab, you will obtain an Encounter Ring. Equip it on any character. This causes you to enter a battle with every step. You will manually have to level at this point until you are strong enough to go through the auto battle sequence. Next, download "The Toucher" app from the Play Store. This is a macro app. Set it to record, and in the game, walk up and down and battle three or four times. Save your new macro and run it. Your characters will walk back and forth, doing battles for as many repetitions as you set it to. For example, use 99,999,999 repetitions and run the macro for one hour. You will earn gold, RSP, and gain experience. Later in the game it will yield much greater rewards, but early on it is a great way to get ahead.