I defeat Rhapthorne for the first time during the game. This is where you get the first of two endings for the game. In this battle the pain in the butt section is where you have to summon each of seven mages by having the whole party pray in unison to the god bird staff. After that it is open season on the purple guy. I used my monster party to speed up the progression of the battle and for some change in venue.
My characters levels are level 45 for the hero, 45 for Yangus, 43 for Jessica, and 44 for Angelo for those who are interested.