The Bride & the Exorcist Knight Vol. 3 (manga)

MONSTER-IN-LAW!

Anne has spent her whole life being menaced by demons, but things have gotten a little easier since 12-year-old exorcist Haru Vellman took her in. Now Anne must face her scariest foe yet...Haru's family! Dorothea, the head of the Vellman clan, sets down a challenge for Anne: if Anne can exorcise a demon that's been lurking in a nearby convent, Dorothea will approve of Haru and Anne's engagement. However, since men aren't allowed inside the convent walls, Anne will have to do it alone, without Haru's help...