Here’s a conversation between Charles and Erik (from my Regency AU, Roses & Cinnamon) that didn’t make it into the final version of the story, because there just wasn’t a natural place to put it. Not spoilery, but you may recognize a few phrases from the final draft. If you’re interested in what war veteran!Charles has to say to vengeance killer!Erik on the subject of killin’ folk, read on.
"You call me a killer," Erik said at last, his voice flat and leaden. "When you have surely killed many more than I, in the war."
That was, perhaps, the very last thing Charles expected, and now he did look up, in surprise. “Yes,” he said after a moment. “To protect myself and my brother-soldiers. To serve my country. It is not the same as a cold-blooded murder; I think you know that. But I know you feel your actions were justified, and…” He rubbed wearily at his eyes. “And the truth is that it is hard to argue. It is not as though a human prison would have held him, a man whose Gift could tear through half a house. But that is not the <i>point</i>, my friend. You may think me naive for arguing against killing such a man, but it is not for his sake that I argue.”
"What do you mean?"
"I saw both sides of the death equation on the battlefield, Erik. I don’t know how to communicate the horror of being surrounded by the wounded and dying, with my Gift. But worse, in its way, was seeing the effect on the survivors. Watching my brothers-in-arms — not all of them, but more than anyone would guess – slowly transform from men into wolves." He held Erik’s gaze. "Humanity is a predator species, Erik. The entire purpose of civilization is to help us forget that. On the battlefield, you have no choice but to remember. The more you learn to live with killing other human beings, the closer the wolf comes to the surface, and the harder it is for the man to ever return. And Erik…" He could not help reaching up to touch Erik’s arm. "The wolf in you is so very loosely contained. I cannot bear the thought of losing you to it entirely."
Erik swallowed. “Then you do not think me lost already?”
"No!" In horrified surprise, Charles did what perhaps he should have done far earlier, and opened his mind to Erik’s. The swirl of self-hatred and despair he found there made him gasp, and he reached out instinctively to soothe it. Not erase it, he had sworn not to modify Erik – he only offered reassurance. The cat-brain leaned into that touch, and, to Charles’s surprise, so did its conscious counterpart, Erik’s eyes fluttering briefly shut. "No, my friend," Charles said softly, "you are not lost at all. I’m very sorry for the things I said, Erik. I still disagree with you ferociously on this issue, but I have already concocted some alternatives that may please us both, if you are willing to hear them." He had not, he realized, released his hold on Erik’s arm, nor had Erik moved away from it. "I am certain we can find a way to compromise."
"Yes. I am certain we can."