The scene shifts back to some time before the incident happened. Woori is lost in the schoolyard while Soo Ji texts Yerim, asking her to meet by the swimming pool. Seung Hwa goes to the rooftop to set up a computer. Yerim ends her performance and receives a message from Eun Jeong congratulating her on her debut, and she breaks down in tears. Soo Ji arrives at the pool and already sees Yerim on the floor. In the class, Do Ah asks Harin to address the class before starting the vote for the 16th. Ha-rin tells the class that they are going to pick out one student as the permanent Rank F student for the entire term until they graduate. She asks if anyone is willing to be the permanent Rank F student and looks at Ja Eun, expecting her to volunteer. At that moment, Soo Ji rushes in and pushes Harin up to the board. Soo Ji confronts Harin about what she did to all the girls, especially to Yerim, who is taken to the hospital. Harin tells Soo Ji to know her place and let Harin continue the game. Soo Ji dismisses Harin's reliability as Harin texted in the group chat that Da Yeon would get punished, but she is still here. Seeing all the girls start to side with Soo Ji, Eun Byeol tells everyone that she is on Harin's side and convinces other girls to follow Harin's idea of having one permanent Rank F. Soo Ji tells everyone that if they do what Harin says, they are voting against their friends and can seriously damage that person's life. She then asks her classmates to delete the application from their phones if they don’t want such a cruel game to continue. Harin and Soo Ji both look at Ja Eun because they know her decision can make a big impact. To Harin's surprise, Ja Eun no longer allows herself to be Harin's scapegoat and deletes the game. A flashback shows Ja Eun overhearing Ha-rin's conversation with Eun Byeol. Ha-rin mentions that she was going to trick Ja Eun to be a Rank F student, which prompts Soo Ji to sacrifice herself, and the only way it won't happen is if Ja Eun no longer accepts herself as a Rank F student and stands up for herself. Harin is shocked by Ja Eun's action, while Soo Ji continues asking everyone to delete the app. One by one, the girls delete the app, and at some point, they only need one more vote to win a majority. At that moment, Da Yeon stands up and proudly deletes it, but Soo Ji says her vote won't be counted because she’s no longer a student in their class and she should leave. Da Yeon loses it and is about to strike Soo Ji, but Ja Eun stops her. Da Yeon gets wild again and starts beating Ja Eun up brutally. And somehow, her attack is being livestreamed. When there is enough evidence, Ja Eun stands up and defends herself. She is much stronger than Da Yeon and quickly holds her down. At that moment, someone deletes the app; it's none other than Do Ah, who is fed up with all the mess the pyramid game caused. It turns out Soo Ji convinced Do Ah to help get rid of the game, and Do Ah finally agrees. She was the person who placed the camera this time, which allowed them to livestream the evidence of Class 5's bullying to the public. And now, with 12 votes out of 22, the game is completely terminated. Meanwhile, Seung-Hwa leaves the rooftop and notices that the livestream video has been deleted. A flashback reveals Soo-Ji asking Seung-Hwa to leak the audio recording before the video recording because it would surely be controlled by Harin's people. She also asks him to check on the teachers due to signs of grade tampering.

In the present, Seung-Hwa sneaks into the teacher's room as all the teachers rush to Class 5 to stop the livestreaming. Mr. Quickly spots it above the board, and Principal Im smashes it under her shoes. However, the video has already reached a large audience and spread everywhere.

Soo-Ji's team meets up on the rooftop and inquires about Yerim. It turns out she is in the hospital but completely fine. A flashback shows Yerim calling Eun-Jeong, then by the swimming pool, the person in a teddy bear mascot approaches her. Just as that person is about to attack Yerim, Woori runs in and knocks her down. Woori chases after the stalker.

Somehow, Yerim's absence has an impact on the vote today, making everyone believe Harin was the person who harmed her. Soo-Ji meets Seung-Hwa and learns that he had stolen some files from Mr. Lim’s computer but found nothing related to school bullying. Meanwhile, Miss Yoon reports the school bullying at Baekyeon High School to the police.

Soo-Ji informs Seung-Hwa that Woori was at their school, and he goes to check on his sister. Seung-Hwa understands that she likely left her room after realizing that Yerim's stalker intended to attack her at the festival, and he's proud of her. All the parents of the girls in Class 5 are shocked by the news. Harin asks her mom to transfer her to another school, but this time, even Harin's grandma is mad at her for being so foolish. Soo Ji's dad asks why she didn't tell him about the bullying, and she says it was he who taught her to deal with problems on her own. She also mentions overhearing him talking with his colleague about a bullying case at the base camp, and he chose to look away.

Meanwhile, Ja Eun's mom visits her, apologizing for not knowing what her daughter had to deal with at school. The next morning, Ja Eun's mom asks her to stay at home and suggests transferring schools, but Ja Eun says things are fine and that she has friends at school. She finds Harin's lighter, and Harin herself is also around the corner. Harin asks Ja Eun if she does not remember what she did wrong in the past, but Ja Eun just gives her back the lighter and leaves.

The school becomes a mess after the livestream. The school violence committee investigates Woo-Yi, Do-Ah, and Seol-Ha. The students of Class 5 are reassigned to new classes. Later, Soo-Ji learns from Do-Ah that Ha-Rin is moving abroad, while Harin’s grandma requests Mr. Baek to protect Ha-Rin from the school violence investigation. Ha-Rin holds her grandma and whispers something into her ear. Yi-Hwa tells Do-Ah’s father that she won't protect Do-Ah and Ha-Rin, and will prioritize the Baekyeon Group's interests first. At a press conference, Yi-Hwa claims the school was unaware of the bullying but is now taking action against it.

Ja Eun tells Soo Ji to go to a place with her, where she will understand the untold story between her and Ha Rin. Ha Rin soon shows up there as well, revealing she was So Won and a victim of bullying. Ha Rin tells them that she orchestrated having the building of Class 5 designed like this place, which used to be her orphanage, and she is an adopted child of the Baekyeon family. A flashback shows a young Ha Rin bringing Ja Eun back to her orphanage and revealing that she doesn’t have parents. Harim learned about the pyramid scheme in class when their teacher asked them about the differences in treatment depending on hierarchical rank, using pictures of the Baekyeon family as examples. Harim didn’t know anything about them and answered only one question correctly, for which her teacher punished her by allowing Harim to eat lunch with just kimchi and sleep without a blanket. Besides, Harim got bullied every day and decided to do something to get out of this place. One day, she overheard the teachers talking about a visit from the Baekyeon family, who were looking for a child to adopt. So, that day she tried to impress Cho Soon with a dance and get adopted. However, her foster parents didn’t like her. Harim soon realized that in order to survive, she had to impress Cho Soon, so she studied hard and acted determined to impress her grandmother. Ja Eun apologizes to Ha Rin, just as the lighter Harin set behind a curtain drops on the floor and the school starts to catch fire.

Ja Eun rushes towards her to help her get up. Meanwhile, firefighters receive the alarm and hurry to the scene. Luckily, the three girls are rescued in time and taken to the hospital. Doah's father hires someone to post an article exposing Harin and her bullying at school. Yi-Hwa confronts him, and he admits that he did it to get revenge on the Baekyeon family for using his daughter as a pawn in this scandal. Yi-Hwa, aware of the fire at the orphanage, decides to coordinate with the school and media to mislead the public. They hire a YouTuber to analyze the footage of the bullying video, cutting out the scene where Soo Ji pushes Harin against the wall. He asserts that Harin is the victim of bullying, while in reality, Soo Ji is actually the bully. Principal Im also discredits Ms. Yoon's report and tells the police that she was just a contract teacher who was poor at her job. Moreover, students who sided with Harin are instructed to lie to the police, claiming that Soo Ji has a violent tendency, just like her military father. Many articles and comments are directed against Soo Ji.

The police come to the school to question her about the fire at the orphanage after finding Harin's lighter at the scene. Soo Ji is soon released, and her dad comes to pick her up. Everyone stays at the convenience store to discuss a way to help Soo Ji. The next day, Jae Hyeong and Ja Eun meet with a reporter to ask for her help in exposing the truth. Ms. Choi overhears them, understands what they are trying to do, and decides to meet up with Ms. Yoon. It's revealed that in September, when she called her boyfriend, Ms. Choi caught the Da Yeon group beating up Soo Ji on camera and recorded it. Ms. Yoon gets the video and posts it online, while other girls from Class 5 spread this video and also speak up about what happened to them. Yerim records a video admitting she was a bystander who didn't stop school bullying, even knowing it could end her music career. Yerim is at the hospital with Eun Jeong and writes "I miss you my friend" on her cast, then sends this picture to Woo Ri, making her super happy. Seung Hwa thinks something happened to his sister and goes to check on her, but Woo Ri is just happy that Yerim cares about her. Here, she tells him about her encounter with Harim at the school festival. Woo Ri gathers all her courage and asks why Harin made her life hell. Harim tells her it was because Woo Ri once unintentionally stepped on her foot. The next day, Woo Ri decides to reveal to the world the absurdity of Harim's bullying and the horrible treatment she received from her teacher, with Seung Hwa’s help to record a video.

Ja Eun also understands what Harim meant when she talked about the reason she bullied Ja Eun. It turns out they met after many years, and Ja Eun approached Harin to say hi. Harim is upset that Ja Eun is still happy and doesn't dwell on the past. Harim wants to torture Ja Eun without knowing what she did wrong.

Later, Ja Eun meets Soo Ji at the convenience store. Soo Ji discovers that Eun Byeol is cheating because the exam and the test inside Mr. Lim's computer had only one question changed, and Eun Byeok asked about that specific question during the exam.

Soon, more scandals at Baekyeon School are exposed, including bullying, cheating, and grade tampering. Mr. Lim, Principal Im, and Yi Hwa are arrested and taken to the police station, while inspectors come to the school to confiscate all papers for investigation.

Da Yeon is continuously beaten up by her father. Woo Yi's parents take her to a mental hospital, and Seol Ha is kicked out of the national taekwondo team. All of them have to prepare to go to court.

Also, the girl in the class who paid to get good grades and the henchgirls on Harim's side are exposed and cannot go to good colleges. Do Ah is also expelled because she is still in the leader group.

Despite all this, they don’t hear anything about Harim. Do Ah goes to meet Soo Ji at the convenience store. Soo Ji feels sorry for her, but Do Ah thinks it’s what she deserves for her wrongdoing. Do Ah's dad is angry that she has ruined her future and wants her to study abroad. However, Do Ah doesn't want to leave and insists on finishing her studies in South Korea, despite having limited options. Furthermore, Do Ah is aware of her dad's affair and uses this information to silence him. Meanwhile Mr. Baek on behalf of his family announces a public apology and declares that they were not aware of Harin psychopathic tendencies and will revoke their adoption of her. They also suspend all their funding to educational projects. Ja Eun tells Ja Eun that even though what Harin did is terrible but she regrets being a bystander back then that led to Harin's villain origin story. Meanwhile Harin is in a mental hospital under a fake name. And Soo Ji thinks it’s the most suitable punishment for Harin, being discriminated and neglected. Soo Ji and Ja Eun choose to never again be a bystander and will always fight against bullies. Two months later, the school is reopened and taken over by a new company named Miryo Group. Seung Hwa enlists in the military and says goodbye to Soo Ji. Soo Ji and her friends go to the school and now they are seniors. In the teacher’s office, the Miryo twins decide they would want to play the pyramid game. And then they are introduced to the class as the series ends.