NTR stands for Netorare. In manhwa, it usually involves a situation where a character's romantic partner is stolen or seduced by someone else, causing emotional distress for the character.
The plot of 'A Class Daughter-in-Law' manhwa is full of twists and turns. It shows how the main character navigates through difficult family situations. Its charm lies in the realistic portrayal of emotions and the growth of the characters.
I'm not sure specifically as there could be many different 'secret class stories'. It could be about a special class that has some hidden knowledge or activities, like a secret art class where they teach unique techniques not known to the public.
I recommend you to read a novel called " Film and Television: Starting from the Little Joy of Time Travel." It's an urban and youthful campus novel. The protagonist of this novel, Yao Ce, also returned to his student days in his third year of high school. He explored some secrets in his new class and pursued his dreams at the same time. There are also some descriptions of school life in this story. I believe it will remind you of those days. I hope you like my recommendation.😗
Since I don't know the specific'secret class story', it could be students who are curious and adventurous. They might be the ones who discover the secret class or are part of it from the start.