Follow this video step by step and u will be gaining levels and mana in no time.
keep in mind you will want to be to 6-1 in the actual plot to unlock Vals ability that i was using in this video and u will want a mage to 75 with skills to +3 star mage with Giga Star+3 would work best but i didnt' realize that till later on.
Also before each fight make sure u get the XP x 3 for one kill and whoever you have sitting on the leader role take that fist kill so that way you get X3 exp for that kill along with anyone that is in the prinny stage effect.
Any questions feel free to ask and i will try to help.
sorry if the video is annoying i used my Windows Phone 7 to record it.
my PSN is S1L3NTN1NJAZ
i dont own any rights to this game i only recorded this video as a learning curve for people to use to help them.