The story begins with a girl attempting self-harm, which Myung Ja-eun tries to stop, but is threatened and injured. Years later, Sung Soo-ji transfers to Baekyeon Girls’ High School and discovers her new class, 2-5, is isolated. Soo-ji learns about the Pyramid Game, where students rank each other, leading to privileges and bullying. She becomes a Rank F outcast and is tormented by classmates, especially Da-yeon. Soo-ji plans to gather evidence and team up with Ja-eun, another outcast. Meanwhile, the mysterious Baek Ha-rin orchestrates the bullying, and Soo-ji seeks a way to survive and challenge the system. Ha-rin, admired by everyone, bullies Ja-eun, who later asks her to stop harming others, especially Soo-ji. In the present, Ha-rin intervenes when Soo-ji is bullied, making Soo-ji suspect she's behind the hierarchy game. Soo-ji plans to end the bullying. She discovers that the school administration and some teachers ignore the bullying. Soo-ji learns about the power dynamics involving Ha-rin and influential families. Mr. Lim, initially seeming supportive, reveals his true nature by attacking Soo-ji. Ja-eun helps Soo-ji escape and exposes Mr. Lim’s exploitation. Finally, Ja-eun agrees to vote in the upcoming Pyramid Game, joining Soo-ji’s plan. In Episode 3 of "Pyramid Game," the results of the monthly game rank Soo-ji at C and Ja-eun at D, while Ji-ae falls to rank F. Soo-ji is relieved, but Ja-eun is concerned for Ji-ae, who was betrayed by her friend Seung-yi. Soo-ji contemplates giving up her mission but decides to continue fighting the system. Ha-rin, appearing virtuous, hides her cruel nature. Soo-ji gradually gains allies, including Ye-rim, but remains suspicious of who voted for her. After discovering Ha-rin’s manipulations, Soo-ji strategizes to break the game by targeting vulnerable students and forming alliances. Despite setbacks, she continues to plan her rebellion against the hierarchy. Soo-ji's suspicions are confirmed: Ye-won led Ja-eun into Ha-rin's trap, but Soo-ji intervenes. Ye-won informs Ha-rin if Soo-ji and Ja-eun annoy her. Ha-rin claims Soo-ji's plan will fail, but Soo-ji prevents Ha-rin from bullying Ja-eun. Ji-ae panics, but Soo-ji believes Ha-rin is unaware of everything and decides to proceed with their plan. Seung-hwa, Woo-ri's brother, joins their cause as a hacker. They blackmail Jae-hyung and befriend Ja-eun for votes. Soo-ji's father attends a school meeting about bullying, shocking everyone. Soo-ji persuades Ye-rim to be ranked F, aiming to expose the system's flaws. Yerim refuses Soo Ji’s idea, feeling threatened. Both receive a message from Seung Yi, who threatens self-harm if Soo Ji doesn’t stop. They rush to Class 5, where Seung Yi cuts her wrist. Harim takes the knife, framing Soo Ji as the villain. Ms. Yoon informs Soo Ji's father about the bullying. Parents witness students blaming Soo Ji. Harim’s mom insists they handle it themselves. Soo Ji is punished, losing her votes. Harim plans to make Ja Eun Rank F, but Soo Ji’s plan to push Yerim to Rank A succeeds. Ms. Yoon resigns after destroying the hidden camera. Soo Ji exposes Ji Ae as an informant and shifts to Plan B. Monthly voting results place Soo Ji and Ja Eun at Rank D, with Yerim and Eun Byeol at Rank A. Harim is still angry. After the monthly vote, Da Yeon suspects Harim manipulated votes, causing tension in Harim's group. Soo Ji realizes Ja Eun's approach of kindness is more effective than manipulation and apologizes to Seung Yi. Soo Ji proposes ending the game since there's no Rank F student, but Da Yeon and Woo Yi resist. Eun Byeol, a Rank A student, behaves superiorly but is rebuked by Soo Ji. Harim, furious, manipulates votes. Soo Ji's father is transferred due to Harim's influence. Harim injures Ja Eun, but Soo Ji vows to defeat her. They gather evidence of bullying and plan to expose Harim. Meanwhile, Harim threatens others and manipulates situations to maintain control. During the school trip, Soo Ji delays revealing Harim's manipulation. Harim confronts Soo Ji about her betrayal. Yerim discovers Harim's coercion of Eun Jeong. Woo Yi accidentally pushes Harim into the pool. Soo Ji's father is transferred due to Harim's influence. During the paintball game, tensions rise as Harim tries to manipulate friendships. Soo Ji's group confronts Harim's manipulation, causing Ja Eun to be left alone. However, during the game, Ji Ae sacrifices herself, revealing the truth about Harim's blackmail. Soo Ji's group exposes Harim's schemes, ending her manipulation. During a school trip, Ja Eun, Soo Ji, and Jae Hyeong reflect on their flaws and bond. Da Yeon's aggression leads to Eun Jeong's injury. School authorities cover up the incident. Soo Ji mobilizes a plan to counter Harim's influence using anonymous chatroom accounts. Da Yeon faces severe consequences from her father's abuse. Harim continues her manipulative tactics, targeting Ja Eun and Soo Ji's father. Soo Ji discovers Harim's machinations and rallies more girls to oppose her. Meanwhile, Woori learns of Yerim's performance. During the school festival, Yerim collapses, and Soo Ji confronts Harim over her responsibility. Before the incident, Woori searches for Soo Ji while Seung Hwa sets up a computer. Yerim, emotional after her performance, receives a message from Eun Jeong. Soo Ji finds Yerim collapsed by the pool. Harin initiates a vote for a permanent Rank F student, targeting Ja Eun. Soo Ji intervenes, urging classmates to reject Harin's cruel game. Ja Eun, empowered, deletes the app, followed by others. Da Yeon's attack on Ja Eun is live-streamed. Eventually, Do Ah deletes the app, ending the game. The fallout exposes bullying, cheating, and corruption. Harin's fate is uncertain, while Do Ah navigates family turmoil. The school undergoes restructuring, and Seung Hwa enlists in the military. Soo Ji and Ja Eun pledge to fight against bullies. The series concludes with the introduction of the new students, the Miryo twin, the daughters of the company now own the school who are planning to play the pyramid game.