Have Amarant in your party and make sure he has learned the Chakra skill. Also, the minimum MP needed for this trick to work is 4 MP. Enter a battle and have Amarant cast Chakra on himself. For 4 MP, he will restore MP equivalent to about 20% of his maximum MP. Continually cast it until you get reached your maximum MP. Since you can do this to other characters in the party as well, you can end up will everyone with maximum MP.