I'll clarify more things.
1. Aros has one brother. Or well, SORA did.
2. Aros didn't actually end humanity yet, though did cause havoc at one point, and soon stopped.
3. She claims to be evil when the worst thing she did was steal a jug of milk.
4. Aros is asexual, having no interest in sex.
5. Aros is invincible. Sora isn't. Though able to possess minds, she can only possess ONE mind. If you defeat Aros, you basically beat up Sora and almost kill her- since she's weak and doesn't know how to fight.
6. Aros came from Purgatory as a symbol and guide to souls that either go to Hell or Heaven. Basically imprisoned there for reasons she never explained.
7. Sora at her death wasn't supposed to die early, giving Aros the chance to give her a life if she became a host for Aros.
8. Sora has regular dark brown hair and green eyes, wearing green. Aros has white hair and red eyes, wearing dark purple mainly.