Phantasy Star IV (Genesis) - Boss 17
Gens v2.12 Movie 11
Chaz - level 44
Rika - level 47
Rune - level 40
Wren - level 41
Not difficult.
Don't forget De-Vars is not evil, he (or she?) is an agent of the Pure Light who is testing you, so holy magic such as Efess will be ineffective. He's also immune to fire magic such as Nafoi or pure physical attacks such as Nazan - note that most advanced weapons you use at the end of game don't do physical damage but another king of damage often called "radiation damage". Rune's Legeon also does radiation damage. Pure energy damage does harm him but is not as effective as against evil bosses, so best Chaz' attack is Crosscut.
He seems to use only physical attacks, so the Barrier I launched was probably useless.