The Reincarnation Slavery of the Wicked Lady

Ulysses, who traveled to another world, had black hair and black eyes that were rare in this world. It is recorded in ancient books that this is proof of being born with extremely high magical power. But after five years of studying in the Holy See, he was unable to use even a hint of magic and was regarded as a useless person. War broke out and the kingdom's western border fell. He became a slave, struggling on the edge of life and death. When he was desperate, he was bought by Lord Marcos and became the personal servant of the arrogant young lady Dolores. With the knowledge and education from his original world, he taught arithmetic and took care of daily life. He gradually gained a foothold in the mansion and gained hope for redemption. But he doesn't know yet that he is not unable to use magic. But what he can touch is the black magic that can only be used by the demons in this world. The demons are moving south, and troubled times are coming. How should he act.