[It's not hard to read between the lines.]

I think he targeted you, Touko. Because you were lonely, and vulnerable. And Syo - she's the part of you that wouldn't be touched, or used, or manipulated. She became everything you couldn't be.

But she's just as young as you are. She lashes out because she thinks it's the only way to keep you safe. And she enjoys it, because it makes her feel powerful.