There's plenty way to level up unit like using cactuar or farming exp in exploration dungeon, instead of those.. You can go to adv vortex for 15 energy it gives roughly 30k exp or equivalent to 3* cactuar. How to do this.. It's simple just take a single unit that you willing to level and bring strong friend assist preferably unit with barage to fasten up the runs. Vortex exp reward is divided to all unit that consist in party, if you only bring one unit means all those reward will added to loner unit. This method maybe not the efficients way but it's doable especially of you have limited time to play like my self. It also nice if you want to level a single unit that left behind or want them to advance higher than the rest. Good luck kupo! Sorry if there's a same guide existed, mod can simply remove this, thank's.