Didn't ask. [ Geralt downs his drink and immediately pours another. ] He's—reluctant. To discuss.

[ Which is not to say Dean will not tell him, but he's avoided the topic unless necessary. He's hoping to search for information first before digging deeper into what else Dean may know. ]

The magic is tied to a mark and a first blade. I assume, according to legend, the blade Cain used to strike his brother down. Obviously, the blade doesn't exist in this world, but the curse holds. So it must originate from the cursed soul itself.

[ Or else it would not have—could not have—followed Dean through the Singularity. ]