Forge many Genius Quills and Halgition papers and write Memoirs of a Mercenary 60 times.
Use 30 on capell.
Use 10 on ed.
Use 10 on touma
Use 20 on Michelle.
This should give capell well over 1 million hp and significantly increase the HP of your other characters.
Its time consuming, but do it this way and the fight is long, but VERY EASY.