When Raven and Charles were little, Raven would sneak into his room to sleep in his bed with him almost every night, because she still didn't feel safe in that big old house with the servants and her new "parents" wandering around.
And most nights she would dream about what her parents had tried to do to her. Raven never remembered these nightmares when she woke up, but they had a way of leaking out of her mind and working their way into Charles's, infecting his own dreams.
So Charles would dream of water running in a bathtub. Of a rough hand on the back of his neck, pushing him under, while another pair of hands twisted his arms behind his back. He'd dream of being drowned, and of breaking away, of blood on white tile.
He'd wake shaking and sobbing from these second-hand nightmares, and Raven would do the best she could to fix whatever it was that was wrong with him, but she didn't understand it.
Even as an adult, Raven never remembers her dreams. If someone asks her about it, she tells them that she doesn't dream, and she believes this is the truth. Azazel knows about the dreams, but he never attempts to wake her from them. The type of terror that spawns those nightmares – the sense of being trapped and helpless – are nearly foreign concepts to the teleporter, something that might happen to others but never to him. Watching Raven twitch and moan in her sleep, fighting demons he can't see, mystifies and frightens Azazel, but he learned very quickly not to touch her when she's in the grip of these battles, because she'll lash out viciously without ever waking.
But when she and Charles were still children, and when he woke up crying, Raven would try to make whatever was wrong better, but she never guessed that she was the source of all of it. She'd get him to tell her stories, or to read to her, anything to take his mind off the badness, and she'd sit up awake with him for as long as he needed to.
Only sometimes she'd get impatient, because school was hell for her and she's always on edge and worn out when she was trying to keep her true self hidden, and all of that was so much harder when she hadn't slept. But he kept waking her up every night and she was so exhausted and so scared that this exhaustion would cause her to make a mistake and someone would see her blue and want to hurt her.
And she didn't get it. She really couldn't understand why Charles was so delicate, why he had such bad dreams when obviously nothing really bad had ever happened to him in his entire life.
Charles never told her. He was Raven's big brother now, and that meant that he had to protect her from everything, even memories that she was trying so hard to forget.