WARNING: SPOILERS
Absolutely!
There's a hidden Relic that mitigates Dark damage (their strongest attacks) and provides a pretty good stat boost. You need all 3 of the dungeon treasures to find it, and the entrance is within 1 screen of the starting area.
Otherwise, the big bad is weak to Holy damage but likes to increase his defensive stats, so finding the right time to use those Light Arrows (which remove certain buffs) is important.
If you took the "light" path after each of the 3 bosses, you can unlock a special power by casting all 3 Summon skills in the same turn using Brave.
"Dark" characters will probably need to keep Steady and Reforge on for as much of the battle as possible, using Resurgence to heal as needed. Blast also removes defensive buffs, if you have it.