Kurotsuki no Yaergnacht

From Kodansha:
While on his way home from an interview, unemployed, unmotivated, jaded 18-year-old Inumata Shinogi encounters the beautiful lady and evil spirit Yaerknacht Finsternnis. She demands he either marry her or die on the spot. He must command the battle against enemies of humanity, the apostles of god (Highlander), and save the world with his wife. Battle fantasy with the infatuated strongest kuudere beauty, start.