Comments of chapter undefined of Bloodbound Devil (Multi-Cross, DxD, Rosaria Vampire, Seikon no Qwaser)

Vampires are in a way similar to Devils in many aspects. If you base it up to DxD magics they call it Demonic Power. Similarly, in Rosario+Vampire the power system calls it yoki (Demonic Energy which you can word it Demonic Power). That's the explanation, I guess.