Episode 4 of "Friendly Rivalry" picks up right where the last left off, with Seul-gi tentatively asking Je-yi if she might join her at their shared table. Je-yi, her face lighting up with genuine pleasure, readily agrees. Meanwhile, Na-ri, Je-yi's former seatmate who had previously bullied Seul-gi, mysteriously skips class, arousing Ye-ri's curiosity and suspicions.
Later in the day, Je-yi boldly nominates Seul-gi for the position of class monitor, a role that Choi Gyeong had been eagerly vying for as a strategic advantage in their university applications. Thanks to Je-yi's unwavering support, Seul-gi emerges victorious in the vote against Choi Gyeong. Fuming with rage, Choi Gyeong throws a fit, insisting that the election had been rigged, yet lacks the evidence to back up her claims. Ultimately, at Je-yi's insistence, Choi Gyeong is compelled to apologize to the class for her outburst.
Elsewhere, Je-yi's father finds himself entangled in accusations of medical negligence but mandates that the matter be resolved discreetly through negotiations.
Meanwhile, Seul-gi persists in her attempts to decipher the password on her father's phone when she receives a message from Je-yi, inviting her to meet. Keeping Seul-gi on tender hooks, Je-yi eventually catches up with her at a karaoke bar before whisking her away for an overnight slumber party at her place.
Concurrently, Ye-ri overhears a hush-hush conversation about Na-ri's family having sold their house for an unusually low price, piquing her interest further.
Back at Je-yi's cozy abode, the two girls bond over their mutual fascination with the enchanting sensation of being submerged underwater, before settling down to rest. That night, Seul-gi is jolted awake from a dream where she and Je-yi share a tender kiss in a bathtub, prompting her to abruptly dash to the bathroom. Upon her return, she catches a glimpse of a message on Je-yi's phone from Na-ri, pleading for forgiveness and requesting the deletion of a video.
The episode draws to a close with Seul-gi reading the message in astonishment, while elsewhere, Choi Gyeong delves deeper into the case against Je-yi's father, determined to uncover the truth behind the allegations of medical negligence.
