Ff13 stuck on dahaka boss please help?

Friend gave me his final fantasy 13 game for the ps3. and im on chapter 11 of it and im fighting a boss called dahaka on the top of taejins tower. i get him below half hp and then he uses a plague attack which puts like 10 debuffs on us and hope refuses to debuff them. i was wondering if there was a quicker way to avoid this and kill him. my characters are lightning feng and hope. they all have lvl 3 skills in they're mains ones (commando rav, sent, and medic,) except for lightning who almost has lvl 4 commando. if someone could tell me what i need to do or what im doing wrong and how to kill him that would be great thanks.