There are many different elements / types of aether, but none of them are explicitly tied to good or evil. Varying enemies and character alignments have used them.
The Ascians have been seen using fire, ice, and dark/shadow aether attacks. DRKs also make use of dark/abyssal skills, and can be as heroic as you want them to be. Voidsent are the enemy type most commonly associated with demonic corrupting darkness tropes.
On the opposite end of the enemy spectrum, the Heavens' Ward knights and the bosses of Amdapor use holy light attacks, like PLDs. Notably, the final boss of Amdapor uses Cure spells as offensive damaging attacks.
Materia types like vitality, elemental, and tenacity can help increase survivability and protection.
The Ascians have been seen using fire, ice, and dark/shadow aether attacks. DRKs also make use of dark/abyssal skills, and can be as heroic as you want them to be. Voidsent are the enemy type most commonly associated with demonic corrupting darkness tropes.
On the opposite end of the enemy spectrum, the Heavens' Ward knights and the bosses of Amdapor use holy light attacks, like PLDs. Notably, the final boss of Amdapor uses Cure spells as offensive damaging attacks.
Materia types like vitality, elemental, and tenacity can help increase survivability and protection.