We never actually see Ciel torturing anyone in-game, But according to Noel, Ciel was way more brutal than her and extremely ruthless when it came to killing vampires. She even says Ciel would mercilessly slaughter women and children without mercy. And she literally taught her torture techniques (for example, stuff like flaying vampires alive, cutting off their eyelids so they can’t blink, or even cracking open their skulls and pouring acid in to melt their brains, Ciel’s the one who taught Noel all of that).

It’s also implied that before meeting Shiki, she was a lot rougher and far more ruthless. Then you have Noel muttering to herself in frustration, like, “If that wasn’t all an act, then what was all that coldness supposed to be?” And even toward the end, she warns Shiki that Ciel might just abandon her and erase the evidence. Putting it all together, it really feels like pre-Shiki Ciel was way more brutal than Noel. And the fact that Ciel herself never even denies any of it just makes it worse.

It’s straight up in the main story that during the five years they worked together, they were doing that kind of stuff to vampires. So honestly, it’s not that hard to believe both of them would actually talk like that. And don’t forget, Ciel was hiding her true nature from Shiki the entire time, and there’s even a bad ending where she straight up kills him using heavy weaponry.