Blue Birthday

What Ha Rin received for her 18th birthday was the death of her first love. 10 years have passed since. One day, when she visits her old neighborhood and retrieves Seo Jun's old photos. Since the photos remind her of the pain, she burns one of them.

When Ha Rin realizes that she had traveled back in time, she looks for Seo Jun. The dreamlike reunion only lasted for so short and she is back to the present. She thinks it was a dream, but soon notices that new memories from the past had been formed.

Ha Rin decides to find out why Seo Jun had committed suicide 10 years ago. She checks what kind of books Seo Jun had rented, reaches out to his friends, and also looks through his social media accounts. In the process, she discovers a shocking truth.

Ha Rin makes up her mind to prevent Seo Jun's death. She goes back to the past to resolve the conflict Seo Jun had with his mother. Although she succeeds, she remembers that she had forgotten the plans she had made with Su Jin, her best friend.

Having fixed the past, Ha Rin enjoys her date with 28-year-old Seo Jun, but she and Su Jin were not on good terms. She also finds out that Seo Jun's older sister Hye Min had passed away. She realizes that someone has to pay for the changes.

Ha Rin manages to save Hye Min from her death. But now that Hye Min is alive, Seo Jun is once again gone. Ha Rin tracks down the clues to Seo Jun's death, and notices some weird things. Once again, she burns another photo to find out the truth.

When Ha Rin finds out that Seo Jun had actually been murdered, she tells Seo Jun who doesn't trust her. Ha Rin tries to figure out the culprit, but she doesn't have much time. She goes through Seo Jun's bag to find more photos.

Ha Rin finds out that Seo Jun had also been traveling through time. He tells her not to come back any more. After coming back to the present, Ha Rin burns another photo. While trying to find more clues, a shelve suddenly collapses on top of Ha Rin.

Ha Rin approaches suspect Shin Woo, but he only gives vague answers. Meanwhile, Ha Rin's friend Eun Seong grows concerned of her obsession. Ha Rin tells Eun Seong everything, and the two sneak into Shin Woo's workplace, and start digging through his car.

Shin Woo is pointed out as the new suspect but he suddenly dies. Ha Rin notices that Shin Woo might have been killed by the same person. She immediately burns another photo and head to the photo room, but the camcorder was now gone.

Ha Rin is heartbroken when Seo Jun is injured. Although distressed, she tries to find further clues. Meanwhile, Ha Rin hears that a man had visited a vet to purchase Follenir, which was used on Seo Jun for his death.

Everyone starts suspecting Su Jin when they find out she was caught on the camcorder. Shortly after, detectives come to arrest her as culprit. Meanwhile, Ha Rin finds out the culprit's traces while calling Eui Yeong on the phone.

Everything was now in peace. Hye Min was arrested and Seo Jun was alive. However, she becomes anxious as Hye Min's sentence nears end. After being released from prison, Hye Min comes to Ha Rin. Right then, she received a phone call.

Ha Rin and Hye Min accidentally travels back in time. Hye Min wakes up at a police station, and Ha Rin starts looking for the knife which is seen nowhere. While Hye Min escapes from the police station, Ha Rin comes across an art student holding the knife.

Seo Jun screams in despair when he loses Ha Rin. He tries to save her, but can't seem to figure out how. He thinks that this is all due to him being alive, and decides to end his life. But just then, he remembers that there was one photograph remaining.

As his consciousness fades, Seo Jun remembers the first time he meets Ha Rin. Ha Rin heads to the police station, where she runs into Hye Min. Watching her smile, Ha Rin experiences uncontrollable anger, and warns her that she will pay for this.