[Does she truly believe that? That dark magic isn't all that bad - aside from appearances, of course? It seems rather unlikely... but Sayaka wouldn'thave come this far in her training if she didn't have some interest in dark magic, so perhaps there's a bit of truth in her words.]

I have, yes. Dark magic has caught my interest; I've been hoping to learn more here.

[That's not the truth, but it's close enough. Saying he's been studying it since childhood would be more accurate, but hardly suitable for the lie he must live for the sake of Lady Edelgard's plans.]

I am surprised that it's something you find interesting... perhaps we'll learn more together.

[Given the smirk he says it with... is that a threat??]