This battle is somewhat difficult. At first, this boss makes use of some elemental Ninjutsus for about 700 damage and his physical attack will damage more than 1000 to a front-row member. When his HP gets lower, his stats are boosted. His Ninjutsu will do about 40% more and he will use attack such as Assassinate or Great Gale to either instantly kill or drop one's HP to critical status.
Two Dancers with Cure Waltz or a White Mage with Curaja should be enough to keep the characters healthy. His attacks are strong, especially when his stats get boosted so healing consecutively is recommended. A Summoner with Tidal Wave, a Black Mage with some strong spells a Monk or a Dark Knight (preferably with Back Liner) along with Jinnai can damage him well. It is a good idea to heal from time to time as this boss changes to Mind Parasite immediately after his HP runs out.