Tou no Igaku-roku – Akuma ni Tsukaeta Maid no Ki summary:
They say that it is the devil who lives in the northern tower. In the north of an empire a girl of foreign blood works as a maid in her lord's castle. One day, however, she is ordered to go to the 'Northern Tower' for an unusual task. There she meets the 'Devil' and, due to his whims, ends up serving at his side from then on. The demon's name was Johann Albrecht, the second son of the castle's owner, Count Jäger, who had been imprisoned for his cruelty. He gives the girl the name of the witch 'Hecate' and teaches her the true meaning of his own name, 'The Devil'. Johann the Devil wants to revolutionise the world, and Hecate begins to help him, inspired by him.