I couldn't finish 'em. Looks like this's gonna get complicated.
Orochi uses various Breath attacks. While its HP is high, it usually cast Tri-Breath on the party. However, under low HP, the boss can use Fire Breath, Thunder Breath and Blizzard Breath consecutively to inflict massive damage. Venom Breath may inflict Poison and Constrict may be used to counter attack. Also, Orochi does multiple physical attacks in a row.
Orochi will triple-casting Fire, Blizzard and Thunder Breath when its HP is depleted enough, which may deal a massive amount of damage, so it's recommended to have one or two healers ready during the battle. Other members may make use of various Abilities, Fusion Abilities and Spells to bring the boss down.