Han Aera was the type of girl no one remembered after graduation. When people looked back on old yearbooks and see her, they would have to rack up their brains to find any trace of her existence, and it still wouldn't be significant enough. 

She was the typical wallflower. 

Her sister, Han Hara on the other hand was so loved by everyone that when you thought of Seoul High School, her face would be the first to pop up in your head. She was captain of the cheerleading squad and girlfriend of the football captain. People envied her life, and oddly enought Aera was the least envious. She was the one who always encouraged her to be active in school and to be confident in whatever she did. It was a bit skeptical why she was so supportive of her more popular and loved sister, but she was sincerely encouraging towards her sister. 

Oh Sehun was the son of the owner of the gigantic high school. Seoul Academy was a school that had grades from k4 all the way to high school. It was the top school in the country and every student either had the brains or the money to enroll. Most of them were there because they were from prominent families, but the others were there on scholarship. Sehun was obviously there because his father was the owner. He was well known and many admired him for his stunning good looks.