Do You Think Someone Like You Could Defeat the Demon Lord?
Flum was part of the hero's party, but she was sold as a slave by one of the members because he tought she was useless. Flum's only ability is called "inversion" and she doesn't know what it does. After becoming a slave, she meets another slave named Milkit. They find themselves in a life-threatening situation, and Flum's ability turns out to inverse the effect of all equipment/magic, so cursed equipment actually improve her stats. She escapes with Milkit, who insists on becoming her slave, because she has never been in any other type of relationship. They become adventurers and meet a young nun called Sierra. They keep encountering weird creatures with no face, whose stats are unreadable and who seem to recognize Flum. After a battle against said creatures, Flum and Sierra pass out, and a demon lady appears who seem to know Flum too.
The Lazy Son and His Naughty Secretary