( At the first sign of a tremble Vash leans forward, flesh and blood gloved hand over Yato's wrist. ) Hey. I know I don't get all the particulars, but it doesn't sound like you wanted any of that to happen. Someone asked you for something and you gave it to them, and when it hurt them in the end you helped put an end to it. If she was kind then she wouldn't want to be a monster, and you absolutely didn't want to hurt her, I can hear that.

( He doesn't know if there's a cure for someone turning into an ayakashi, he's not going to ask. That would cause more harm than good, and he knows all about having to act in the moment. ) You didn't do it on purpose. It sounds like it was a situation out of your control. Your sister - did she know what would happen?