I've gotten Ifrit Prime to 12% on RDM/NIN on normal difficulty. He's got an instant kill combination that he pulls off eventually due to the long battle times, but I'm sure I can kill him if I try him enough times that he doesn't ever try it. After Firaja (~1000), I can either Cure IV myself or Utsusemi before his next attack. If I Cure IV, a physical + Flaming Crush (~1700 combined if no shadows are up) will kill me. If I Utsusemi, a Meteor Strike (~1000) will kill me.