20th Century Girl (2022) first introduces us to a young woman in a booth as she records for an advertisement in Seoul. This is Na Bo-ra (Han Hyo-joo), whose father calls to inform her that a package in her name has been sent to her childhood home in Cheongju.
Flashback to 1999, when young Bo-ra (Kim Yoo-jung) is in high school. Her best friend, Yeon-du (Roh Yoon-seo) is preparing to get an urgent heart surgery for which she will have to stay in America for some time. Before she leaves, Yeon-du shares a secret with Bo-ra: Yeon-du has a crush on a stranger she met at her parents’ tailor shop. The object of her affections is Baek Hyun-jin (Park Jung-woo), and Bo-ra promises Yeon-du that she will find out everything she can about Hyun-jin while Yeon-du is abroad.
Bo-ra keeps an eye on Hyun-jin and discovers he spends much of his time with his best friend Poong Woon-ho (Byeon Woo-seok). The three start spending more time together, and Bo-ra and Woon-ho discover a shared interest in filmmaking and broadcasting. Bo-ra develops a crush on Woon-ho, who clearly likes her too. But things get complicated when Hyun-jin starts falling for Bo-ra. Through these three characters, the film brings to life the exhilaration and awkwardness that characterise a first love.
Everything goes for a spin when Yeon-du returns, bringing with her a twist to the tale. The boy with whom Yeon-du fell in love at first sight is in fact Woon-ho, who happened to be wearing Hyun-jin's uniform on the day they met. (Discerning viewers may have figured this out already.) Yeon-du finds it funny that Bo-ra was giving her information about the wrong guy all this time, but Bo-ra is devastated when she realises that she and her bestie are both in love with the same boy. Bo-ra encourages Yeon-du to go on the date with Woon-ho in her place, and distances herself from Woon-ho.
Yeon-du eventually confronts Bo-ra about the deception in a scene that’s less about the love triangle and more about the power of female friendships. "I really like Poong Woon-ho," Yeon-du tells Bo-ra. "But if he gets in the way of our friendship, I can let go of him a hundred or even a thousand times. I care the most about you." Yeon-du then tells Woon-ho of Bo-ra's feelings and encourages Bo-ra to bid a final farewell to Woon-ho, who is about to leave South Korea to live with his mother and younger brother in New Zealand. Bo-ra rushes to meet Woon-ho at the railway station, and what follows is a heart-warming confession of love and desperate promises to keep in touch. If the film ended here, there would be no complaints on our end. But there are still 30 minutes to go.
Bo-ra and Woon-ho stay in touch, until one day, his emails stop without explanation. Bo-ra feels blindsided.
The film now returns to the present. Bo-ra is back in her hometown, where she opens the package that’s been sent to her. It contains a videotape and a postcard of scenic New Zealand, signed by someone called Joseph. The postcard also has the details of an exhibition in the area. Curious, Bo-ra visits the exhibition, which has on display videos made by Woon-ho during his high school days. The film ends with the following phrase on screen: “The Eternal Spring. Remembering Poong Woon-ho (1983-2001).”
We learn Joseph is Joon-ho, Woon-ho’s younger brother. He reveals the package was something Woon-ho had stashed away, and which Joon-ho chanced upon more than 15 years after Woon-ho’s passing.
In the final scene of the film, Bo-ra watches the videotape that Woon-ho had put together for her, the one he never got to give her. It is a time capsule of Woon-ho’s 1999, and all the memories he made that year. Bo-ra smiles wistfully as she watches the film, which features candid shots of Bo-ra captured through Woon-ho’s adoring gaze. Towards the end, Woon-ho films the sunrise on New Year’s Day and says into the camera, “Wait just a bit longer. I want to see you, Bo-ra of the 21st century.” The title of the film appears on screen, a melancholic reminder that Woon-ho never got to see Bo-ra again. For him, she will always be a 20th century girl.