Maou no Kizahashi

In the 13th century in Europe, the country of Lublin darkened in the darkness following the invasion of its neighbor, the Grand Duchy of Russo. Stephan, one of the children of the King of Lublin, is the only survivor. He will be picked up by his uncle and fall in love with his daughter. But in wanting to kiss him, he will wake up something dark that had slumbered in him since the attack on his country.