The fifth episode of Dear X opens with Ah-jin walking the red carpet at the Busan International Film Festival, accompanied by the esteemed actor Heo In-gang, whose current love interest is fellow co-star Le-na. However, we soon witness a split between them as In-gang makes a formal announcement of his breakup to CEO Seo Mi-ri. Distressed by Ah-jin's proximity to her ex, Le-na resorts to bullying tactics on set, forcing her to redo a scene repeatedly.
Meanwhile, Mi-ri meets with In-gang and learns his intentions. A call from Ah-jin prompts her to intervene on set, threatening to expose Le-na's past DUI scandal (where someone else took the fall) to get her to behave.
Ah-jin's manager, Hyang-i, reveals to her that Mi-ri maintains a "Shackles Files" containing blackmail material on each actor, kept in a desk drawer. Later, Ah-jin and Le-na cross paths at a salon, exchanging heated words.
Elsewhere, Jae-oh is released from prison and encounters Ah-jin while working as a deliveryman. Though he doesn't reveal himself immediately, Joon-seo, the well-known author known by the pen name Yoon Seok-ha, has written a book titled Co-Offender Y, which seems to chronicle Ah-jin's story.
Ji-sun, burdened by loan sharks, begs Joon-seo's grandfather for financial assistance but is rejected and thrown out. Jae-oh visits his aunt and gives her some money for taking care of his brother, Jae-woong. However, she sends him away as she doesn't want Jae-woong to confront the person who killed his father.
After an interview with a reporter, Joon-seo watches Ah-jin during a film shoot. Her mother finds him there and drags him away, berating him for pursuing Ah-jin again. Le-na overhears this exchange and Joon-seo takes it upon himself to tell his mother off for not yet apologizing to Ah-jin.
Ji-sun storms into the entertainment agency's office, her eyes blazing as she confronts Mi-ri. She demands the CEO to take Ah-jin off the screens, citing her nefarious past of murdering her father. As Ji-sun departs, Ah-jin enters the scene.
Le-na skillfully arranges an event with Joon-seo, flirting with him effortlessly. After the event, she asks him to drop her off at home. Meanwhile, Hyang-i informs Ah-jin of an electrical blackout at the office building. Ah-jin persuades Hyang-i to drop her at the office and head home early, texting Le-na about it. Le-na, in turn, informs Joon-seo to stop by the office for a few minutes.
Ah-jin arrives at the office, climbs the stairs, and starts searching for the Shackles Files. She eventually discovers a secret room with a safe but is unable to open it. That's when Le-na reveals herself, showing that she has taken both their files. Ah-jin follows her down to the parking lot where Le-na taunts her, even slapping her. Joon-seo steps out of his car to witness this, but Le-na pulls him away.
While having a drink, Le-na invites Joon-seo to be her date for Longstar Entertainment's anniversary party, claiming she wants to make her ex-boyfriend jealous and telling Joon-seo that Ah-jin will also be there.
The day of the party arrives, and as the celebrations continue, In-gang begins to feel some pain and struggles to open his bottle of pills. Ah-jin comes to his aid. Joon-seo has indeed come to the event as Le-na's date.
As a dedication video begins to play on screen, it suddenly switches to a clip of Le-na hitting Ah-jin. Mi-ri hastily shuts down the video and dismisses it as a fictional scene from a film, but the tension in the room is palpable.
A flashback scene unveils that Ah-jin had already discovered Hyang-i's collaboration with Le-na. She cunningly persuaded Hyang-i to record the entire incident in the parking lot, ensuring a contingency plan in case things went awry. Presently, Ah-jin issues a stern warning to Le-na, threatening to expose the video if she crosses her. With a purposeful stride, she re-enters the party, only to bump into Detective Park, who had previously attempted to arrest her for her father's murder. Disguised as a waiter, he informs Ah-jin that he hasn't given up on his pursuit. Le-na catches their interaction and sends a snapshot of the detective to a mysterious figure, instructing him to delve deeper. Joon-seo overhears this exchange.
That night, Joon-seo returns home to find Ah-jin waiting for him. This time, their greeting is a tight embrace that speaks volumes of unspoken emotions. Joon-seo thinks she has found peace, but she confesses that she is still struggling. She implores Joon-seo for help and reveals her efforts to cultivate love towards Heo In-gang.
