Shukfir
Auto-translated
I'm a bit confused: if Nicholas knew that the griffin's heart only sends demons back home (in the scene where he was killed, he said, "Come, demon lord, I swear by my father's soul, I will send you back to the cleansing hell!"), then why did he use it at all?
Well, as an alternative, they could have fought the demons and died along with their entire army. But with the heart, there was less blood and less death.
And in general, demons are impossible to kill. Even if their bodies are dead, their souls still return to Shio, where they are reborn as small imps from the wombs.