[ In truth, Sebastian is genuinely impressed for a moment, and it's something he lets show on his face rather openly. That actually is quite a clever solution, and he's surprised that she thought of it. It's likely not something he even he would notice if the blood had been offered to him instead. Though... His taste in sacrifice did tend to be a bit less subtle than that. For a brief moment, Sebastian thins it's almost a shame that she were born so late. Long, long ago, perhaps she may have been quite the witch indeed.

That guilty expression gets him to reach out and place a gentle hand on her shoulder. It's comforting, and it's a gesture to physically express that he's not mad or upset about her giving it up. ]

...Well. I do not know of this spirit in particular, but I must admit, that is quite clever.

[ He does feel like she deserves praise for that, since caution is something he wants to foster here. Her soul isn't something that he has any stake in or claim to, but he's treating it with just as much protectiveness as if that were the case. If she were to contract with a creature even similar to him... It would be a problem. He could imagine countless scenarios where that conflict would immediately have them at odds, and as such, he'll be her protector. It's in a strange way, but at least functionally, she couldn't ask for a better guard against any spirits that might take advantage of her naivete. ]

Do you know why he wanted it at all? [ Then, after a thoughtful noise, he adds: ] Perhaps I should teach you what I know of such things, I realize.