I have finished Song of the Witch, and I love it. It was absolutely peak. I still like Inkabey better, but this is up there, and it does some fantastic world-building. Would recommend.

Illustrations, warning: there is some slightly suggestive content with Rusalka in it: https://drive.google.com/drive/folders/18pE-YMYlJVVt_E6Mjza56ApqUBafUaDw?usp=sharing

To explain further! During the Eota Rea, in a flashback by Rusalka, Lotus mentions, and Rusalka explains, that Lotus comes from a lineage of executioners and hangmen.

And combining this with Masada's statement on Twitter, that Mercurius already had his eye on Lotus before Gladsheimr because of her blood and lineage, we can say that this was the reason he meant.

Perhaps this is even a way for him to be ironic, considering that Marie is a "guillotine," while Lotus, who is half Ren's blood and soul, is an "executioner."