So the beginning of the manhwa shows Jeongmin Choi's (black haired girl) lucid dreams, a lucid dream is a dream you have complete control of. And, in that dream it's basically her bullying this one girl (white haired girl) called Juhyeon. However, once she wakes up from this dream she enters school and you can see how everything that occurs in the lucid dream (shown at the beginning of the chapter) is actually the other way around. Infact, Juhyeon, the white haired girl is the one bullying Jeongmin Choi, black haired girl. The elementary school part, showing Jeongmin and Juhyeon when they were younger is basically why the white haired girl bullies Jeongmin later on in her high school life. It's pretty much the bully playing the victim card as Juhyeon was technically the bi*** that made Jeongmin no longer wanna be friends with her in elementary.
doubt you'll read that but it's basically a long summary of the chapter
i use a different account now may come back to this one never