Based on the doujin by the same name.
In this word, people's abilities are determined by their class. You can change and grow your class through hard work, but there are people called "Class change specialists". With a few rare materials of any kind, a Class change specialist can improve a person's class into a better, new one.
But "The house of evil class change" is run by a succubus named sora, who infiltrated human society and wants to change people into perverted versions of their class.
In this specific version, it uses the evil class change items from the manga.