Fast Level Up:
     There  are  three  items in this game that will allow you to gain
levels at an amazing rate.

Learning Ring:Increases EXP by 30%.
Coin of Fortune:Increases EXP by 50%.
Book of Refining Gold:Turns each Monster into at least 10 Mystic Gems. 

     So,  from  this you can see that if you have a character equipped
with  2  Learning  Rings  and  a  Coin of Fortune they will be getting
roughly double the rate of experience that everyone else is. This will
allow you to get a Character like Valkyrie to the high levels up fast.