In the ninth episode of "In Your Radiant Season," the story unfolds with Ha-ran inquiring from Chan about the pens. Chan shares that he had come across a similar pen in the States and was taken aback by the resemblance. Upon returning to the US, he procured a new one and had it engraved. Ha-ran seems content with this explanation and forgives him for his earlier deception.
Elsewhere, Na-na informs Mr. Park of her intention to retire and travel to France. She claims that the hospital visit was merely a routine checkup. At home, Chan is burdened with guilt for lying to Ha-ran. Suddenly, he hears a metallic clicking sound, which appears to be another clue to his missing memories.
Tae-suk awakens in his apartment to find Ha-young preparing a meal for him. She confides that she thought he had feelings for her and candidly states that she likes him. He clarifies that he doesn't see her in that light, which prompts her to encourage him to start doing so from now on. After she departs, Tae-suk appears somewhat conflicted.
At the hospital, You-gyum informs Ha-dam that her foot will heal within a week. Although Ha-dam expresses concern, he urges her to focus on her studies.
At the atelier, Na-na delegates more of her workload to Ha-ran and entrusts her with managing the visuals for the fashion editorial. Following the meeting, Na-na gazes at the mysterious contents of her locked cabinet and wonders if she has sufficient time. Ha-young encounters Tae-suk in the elevator and shares a barrage of information about herself.
As a new script necessitates a scene featuring the Milky Way, Chan decides to venture out and witness it for real. Ha-ran accompanies him to a campsite where they gaze at the stars. While conversing, Chan experiences temporary hearing loss for a few seconds. Upon returning home, he begins to write about his story with Ha-ran.
The following morning, Ha-dam's family wishes her luck for her exams and sends her off. She stops by the hospital to visit You-gyum and is shocked to learn that he is about to undergo surgery soon. The injury is more severe than what he had told her, and she is moved to skip her exams. However, You-gyum urges her to proceed with them.
Ha-young, filled with enthusiasm, walks into work and begins chatting with Tae-suk. He reiterates his non-romantic stance towards her, making it clear once again.
Chan visits the psychiatrist, who attributes his temporary memory loss to the stress of lying. Desperate to share the truth with Ha-ran, he first seeks to fill in the gaps of his memory. He meets with Su-jin at the hospital and asks what she knows. She claims ignorance, but a flashback reveals her entering the lab that day to find Chan in the midst of a heated argument with Hyeok-chan. Apparently, Chan had been using his identity to speak with Ha-ran.
Presently, Chan returns to the cafe where Ha-ran notices a message from his father on his phone, wishing him a happy birthday in advance. Inspired, Ha-ran decides to plan something special for Chan and makes it quite obvious.
The next day, Na-na and Mr. Park embark on a journey to explore their hometown in Chuncheon. Na-na's house is gone, but the tree from one of their old pictures still stands. They recreate the image and enjoy a good time together until Mr. Park steps away for a moment and returns to find Na-na missing.
With her CSAT exams completed, Ha-dam devotes her time to devising a plan for You-gyum's recovery and shares it with him. Suddenly, he receives a call from someone who says they've found Na-na, who appears lost. You-gyum asks Ha-dam to buy some fruit and then calls Na-na's phone. Mr. Park picks up and You-gyum tells him where Na-na is currently located. Mr. Park goes to a cafe and reunites with Na-na, but her mind doesn't seem focused on the present.
At the office, as Ha-young is about to be crushed by a falling cabinet, Tae-suk steps in and saves her. The two sit down for a drink and she brings up all the incidents that have occurred between them. However, he insists that he only acted because she is Na-na's family. She accepts this with a smile and tells him to leave. Later, she breaks down in tears.
A flashback reveals that Tae-suk was supposed to drive Ha-young's family on the day of the accident, but he was in the hospital with a high fever and couldn't go. Now, he seems to blame himself for her parents' death.
Meanwhile, Chan and Ha-ran are eager to meet for his birthday dinner. On the way, Chan hears the sound from his memories and realizes it was the click of a lighter. He remembers that Hyeok-chan used to fidget with a lighter and suddenly, his vision gets blurry. When Ha-ran calls him, someone else picks up and tells her that Chan is in the hospital. There, she overhears the doctors talking about a piece of shrapnel stuck in Chan's head. She asks him about it when he wakes up and he agrees to tell her everything but says he needs some time.
While he's getting a checkup, Ha-ran waits outside and ends up bumping into Su-jin, dropping all her things. As Su-jin recognizes her, Chan comes out and calls out to Ha-ran. The episode ends with the three of them looking at each other.
