Sennen Sensou Aigis: Gekka no Hanayome

Many years after the goddess Aigis brought an end to the battle between humans and demons, the prince of Logres, descendant of the hero, was living a peaceful life. On one such day, his fiancée, the eastern princess Kaguya, came to him. But before they had time to worry about discussing marriage, demons appeared, and the royal capital was seized in the face of their might. The prince and his allies narrowly escape with Kaguya, and decide to retake the capital.

(Source: Harem-Battle)