The spell to draw out darkblood is already blood magic.

[that's said in a droll tone, as the erune adjusts the blankets around him, wishing that his omen were here, but no. zuoyou is downstairs, guarding the entrance to the basement so no one can disturb his makeshift workshop.]

Blood magic is also one of the few branches practiced in this whole world. You either adapt and learn, or fall behind. [it's a roundabout way of saying that he finds figaro's question utterly stupid.]