Devil Union

The merger of a human with their devil: full power for a limited time. Asta and Liebe are the only pair to enter it as equals.

Nacht teaches Asta the technique in the Underworld: normally the mage dominates the devil and pays the price in years of life or parts of their body. Between Asta and Liebe there is no domination — there is an agreement, and that is why their Union holds longer than any other.