Ebony and Ivory will make them block or outright retreat; making them block leaves them suseptible to the Ophion [Demon Pull]. From here you have an option select to either quickly fire Arbiter's [Flush] for ranged damage or use Ophion again to pull the devil closer. At melee range, be ready to dodge at a moment's notice but Rebellion should work wonders, even using to first two hits of [Hacker] to cancel into [Trinity Smash] or Rebllion's [High Time]. You can get fancy, but remember that the more hits you dish out, the more chances these guys have to earn a parry.

You don't want them to parry.

If they disappear into the void, you have two realities to take note of; inevitable rolling attack or beneficial loss of aggression. Every now and again they'll just stop if you're lucky and hide in their pocket dimension, waiting for you to get closer to where they disappeared from before re-engaging with you. Exploit that at your own discretion. As for the rolling attack, use [Demon Evade] if you've got the timing down for a quick damage buff - [Angel Evade] if there's no room for mistakes.

I personally like to use [Overdrive], [Flush], and [Aerial Rave].

TL;DR:
1. Ebony and Ivory > Demon Pull > Demon Pull > High Time > Aeriel Rave (-1) > Helm Breaker
2. Ebony and Ivory > Demon Pull > Flush
3. Ebony and Ivory > Demon Pull > Demon Pull > Hacker (-2) > Trinity Smash
4. Demon Evade > Overdrive > Flush

Do NOT:

• Throw a blind [Flush]. They'll send it back most of the time. You can parry that if you're ballsy, but this is a guide for simplicity.
  
• Use Roulette. Don't know what it is, but this move loves to provoke a parry even mid combo.
  
• Use Osiris. Low damage, multi-hitting weapon is the last thing you want to kill these fast.
  
• Over-commit. Unless you're in Devil Trigger, there is NO REASON for you to throw more than a couple of blows per exchange. You want to live? Keep it simple. You want to look good? Find a better guide.
  
• Panic. Honestly, these guys are almost fun in a one on one. When you see two of them with a Witch in the room, then you can start signing your will. Let the record show you want to Devil Trigger and kill her IMMEDIATELY in that situation, FYI.