One
Now, you are more than one.
Now you are schizophrenic. (This is not yet a word. It will be, after you are dead. Pay attention.)
Being in two minds about the same thing was strange, but not impossible. It didn't hurt this much. (For years and years and years you will be one. It will be your definition.) It's why the second one turned cruel, why the darkness filled her up and turned her mind. That was the warning, a symptom of the horror that emerges when the line becomes confused.
You have always existed, in each moment, but always separated by time. Your mind (minds, you will contain so many thoughts) knew their place in the scheme of things.
But now you are not Slayer, now you are plural; and it hurts so very, very much.
Each of them (you) in turn, goes mad, sees terrible things that never were and never should be. This is justice, a punishment for those who should never have existed.
You cannot hold forever, eventually you will fail, and the world will collapse. The darkness is multiplied now, and the demon inside is stronger than ever. Did the little blonde (you) know this? And your venom turns towards the one that is Watcher (not was, that kind are never `was'), because you were not made to think. Someone should have stopped her (you).
You can hear them, all the thoughts, and they seem to grow louder with each heartbeat. So very, very many of you now. All the girls who never were, who should never have felt your power.
This is what you will do:
You will focus, find the girl who should have been. You will fight her mind, win (because you always win, it defines you) and take her body for your own. And then the line must be restored, cleansed in bitter blood.
You are one, you are one and one and one alone. It will be swift and glorious, because stability is needed above all else. And then you will not hurt, and you will be whole, and you will sleep again. Alone, the way you were meant to.