In the tenth episode of Dear X, Do Moon-hyuk's proposal to Ah-jin is met with laughter as he slides a ring onto her finger, promising her anything she desires. As he makes this bold declaration, Jun-seo and Jae-oh narrowly escape the burning building orchestrated by Moon-hyuk's minions. Although they emerge unscathed, their concern grows when they lose contact with Ah-jin. Jun-seo receives a call informing him of his grandfather's critical condition and rushes to the hospital, where the elderly man soon passes away.
At the funeral, Ji-sun's presence draws several stares, and Jae-oh arrives to reassure Jun-seo that Ah-jin is safe. Meanwhile, at a luxury bag shop, Sung-hee attempts to resell Ah-jin's bags but is soon met with the arrival of the police, who take her to the station. Ah-jin pretends she had given her the bags and secures Sung-hee's release. Upon returning home, the two engage in another heated argument.
Amidst the chaos, a heavily intoxicated Ji-sun erupts at the funeral when she realizes the old man's will did not include her. In her rage, she reveals that Jun-seo does not share blood with his grandfather. She even accuses Ah-jin of knowing this secret and using it as leverage against her. When Jun-seo questions her motive, Ji-sun asserts that she wanted to shield him from poverty and provide him with a suitable father figure. Jun-seo, in turn, implies that Ji-sun only raised him as an heir so she could inherit his grandfather's fortune, leading him to blame himself for Ah-jin's suffering (the logic here being somewhat ambiguous but serves to underscore Jun-seo's guilt).
That fateful night, Sung-hee burst into Ah-jin's room with a fury, relentlessly unearthing every bitter memory from their school days. Despite the passage of years, her quest for an apology burned within her. But Ah-jin, unrepentant, offered no concession, blaming Sung-hee for the fallout.
Time later, Jun-seo made a visit to Ah-jin's residence, only to find her elusive on the phone. Confronting her about his true paternity, she defended her silence, claiming it was for his own good. Unaware of the truth, he had received the support of his grandfather and blossomed into the writer he is today. He retorted that if she had not lied, he would have known he was the cause of her trauma and would have done anything to make amends.
In a later scene, we witness Ah-jin relocating to Moon-hyuk's mansion, where she is led to her bedroom. On the bed lies an invitation to her wedding in Italy with Do-hyuk. The wedding ceremony unfolds, and we see Jae-oh gazing lovelornly at an announcement on the TV. His boss, Ahn Do-kang, urges him to move on.
As for Jun-seo, he receives a call from Le-na and meets her at the airport. She's embarking on a long journey and advises Jun-seo to leave Ah-jin behind and live freely. He vows to let go of her and his writing as well.
Ah-jin enjoys her life in Do-hyuk's mansion, but soon stumbles upon a locked door leading to the third-floor study. She requests the head housekeeper, Madame Gong, to unlock it, but she asserts that only the CEO has access.
That evening, Ah-jin and Do-hyuk dine together, discussing the new movie he's secured for her. She tries to ask him for permission to use his study to rehearse her lines, but instead, he offers to practice with her himself. She pulls out her script, which revolves around a man who has murdered the protagonist's family. Do-hyuk then begins talking about his ex-wife, who started to accuse him of trivial matters and eventually descended into madness, ending up in a psychiatric hospital. He blames himself for giving her too much of everything. Could this be a subtle warning for Ah-jin? During the shoot for her next blockbuster film, Ah-jin overhears two staff members whispering about how Do-hyuk pulled strings for her and how she probably married him solely for his wealth.
Upon returning home, Ah-jin discovers that menstrual pads are unattainable, prompting her to retreat to the shower for solace. Emerging from her solitude, she finds a box of pads miraculously appearing on the counter. Later, when Do-hyuk returns from his work, Ah-jin notices one of the clocks has stopped working—it's the exact moment her father was beating her, mere moments before she committed the act. That night, Ah-jin wakes up from a troubled dream, reaching for a cigarette to steady her nerves. Meanwhile, Jun-seo invites Jae-oh out for a drink, urging him to live his life freely and avoid the same fate he's suffered. The next day, Jun-seo returns to his mother's house.
One day, Ah-jin catches Jae-oh lurking around and enlists her manager to arrange a meeting. Jae-oh inquires if she's feeling ill and exhausted, and Ah-jin asks him to investigate Do-hyuk and his ex-wife. Unfortunately, Do-hyuk has bugged her car, eavesdropping on their every word. At home, Madam Gong brings Ah-jin a cup of tea, insisting she drink it as Do-hyuk had instructed. Ah-jin throws it in the sink in defiance. The next day, it's revealed that one of the staff members at the house is none other than Sim Sung-hee. As Ah-jin listens to music on a poolside chair, Sung-hee sneaks up behind her and pulls out a knife.
Ah-jin opens her eyes in time, and the two engage in a fierce struggle. Sung-hee is determined to carve up Ah-jin's face to ruin her career, but Ah-jin swiftly turns the knife around and slashes Sung-hee's face instead. The episode ends with Do-hyuk stumbling upon the scene to find Ah-jin laughing maniacally while Sung-hee screams in horror.
