He's got 8400 hp and can absorb fire. Try not to use ifrit although I would suggest to use all the other summons. Bio helps but that dosen't mean it will win you the fight. You should go fight a random battle somewhere else and get full limit bars for everyone before fighting the MK. When the battle starts wail your limit breaks and then cast bio. Have the enemy skill on and learn/use trine. When possible use summons (not ifrit) and when your low on powerful moves start attacking and using Ice or bolt. Always heal your Hp with cure or potions. If you can't knock him dead and get game over I'd suggest:

Level up.