In a different world from the one they live now (Raven's home-world):
Nyx was Raven's mother. Since Nyx could not be present for Raven when she was growing up (even if they were just some walls apart), she took in a young devil (who had pure heart) named Skylar. Nyx, as the ruler of pure(not evil) gods, trained Skylar to be strong enough to guard Raven and her siblings until they were able to stand up in their own power.
Nyx died in a battle against Raven's father.
Skylar was devastated but had to carry on.
Skylar went to earth to take care of Raven until she got used to earth and her destructive powers and trained her as well.
Raven's father sent soldiers to hunt them down and Skylar died protecting Raven.
Now Raven continues untill she brings down her father and avenges her mother and her older sister-like friend.
I won't spoil it more, I said already too much! : )
![](https://s2.save4k.ru/pic/V341KEzGdU8/maxresdefault.jpg)