After a tragic accident, Sol loses her will to live. Sun-jae, the lead singer of the band Eclipse, becomes her only source of hope. On the last day of 2022, she attends his concert, but a few hours later, she hears of his sudden death. Overwhelmed with grief, Sol slips back in time to 2008, returning to her 19-year-old self—when Sun-jae was still alive.

Back in 2008, Sol tries to get close to Sun-jae to protect him, but her efforts repeatedly fail. As Sun-jae, then a devoted swimmer, nears a major competition, Sol fears that preventing an injury he originally suffered might change his life—and possibly save him in the future.

After the swimming competition, Sun-jae invites Sol to dinner as an excuse for a date, planning to confess his long-standing feelings for her. Sol remains unsure if she has truly changed his destiny, while Tae-sung grows increasingly curious about her unpredictable behavior.

Back in the present, Sol discovers the timeline has changed. Understanding how time slips work, she returns to 2008 again—only to find that her 19-year-old self has stirred up chaos in her absence, leaving her utterly shocked. Meanwhile, Sun-jae feels betrayed by Sol’s sudden dating Tae-sung the day after their kiss, and struggles with his feelings.

Sol learns that Sun-jae was the one who saved her from the past accident. Just as he saved her in the past, she feels it is her destiny to save him this time. Sun-jae, believing Tae-sung is using Sol, becomes defensive. As rivalry grows between Sun-jae and Tae-sung, Sol grows anxious with Park Tae-hwan's swimming competition approaching fearing another accident for Sun-jae.

After learning the truth about Tae-sung's intention behind, Sol ends their relationship. Tae-sung is confused by his unexpected emotions after being dumped by Sol. Meanwhile, Sol finds Sun-jae's heartfelt confession recorded on an MP3, which makes her start feeling conscious of him in a new light.

Can destiny be changed? Sol faces the reoccurrence of the tragic Ju-yang reservoir incident. Desperate to escape from this fate, she warns Sun-jae, who remembers her words and rushes to the scene. After a chaotic chain of events, Sol wakes up back in the present! Is Sun-jae still alive in 2023?

After 15 years, Sol and Sun-jae reunite. Fearing he might fall into despair again, she decides to stay by his side after the concert, which is on the last day of 2022, and makes every effort to stay with him through the night. Sun-jae is curious about Sol’s intentions as they end up at a hotel—will they spend the night safely?

The cycle of fate repeats once more. Sol realizes that she was partly responsible for Sun-jae's death. However, there’s one last chance for a time slip left on Sun-jae's watch. To prevent the tragedy she caused, Sol slips back in time to save Sun-jae. However, slipping back once again, she finds herself in 2009 this time, a 20-year-old university student!

Sol confesses to Sun-jae that she’s from the future in 2023, but he misunderstands it as a lie to reject him. Sol, afraid of Sun-jae encountering Kim Young-soo, pushes him away, wishing he’d leave for his safety. Sun-jae, unable to sort out his feelings for Sol, feels hurt and confused.

Sol and Sun-jae finally open up about their feelings for each other. They promise to meet again in the future and decide to cherish the moments they have until Sol returns to the future. Meanwhile, Detective Kim pursues Kim Young-soo based on clues Sol provided. Will Sol succeed in apprehending Kim Young-soo and change destiny?

During the arrest, Kim Young-soo escapes, leaving Sol anxious. She secretly asks Detective Kim's help to prepare for any future incidents, without Sun-jae knowing. Sensing Sol is hiding something, Sun-jae vows to protect her. Sol, Sun-jae, and Tae-sung travel to find In-hyuk, who fled after deciding to quit music.

Sol, having seen the changed future, deceives Sun-jae and stays in Danpo-ri to lure out Kim Young-soo, asking Detective Kim for backup. After she disappears into the future, Sun-jae realizes her sacrifice and rushes back to Danpo-ri.

At the awards ceremony, Sol meets Sun-jae again, who has lost all his memories. Fearing a repeat of past triangles, Sol tries to avoid him. Sun-jae, reading Sol’s script, feels inexplicably moved as the scenes seem familiar and bring him to tears. Every time he sees Sol, he feels oddly connected to her.

Sun-jae takes her home and nurses her as Sol collapses in the Ferris wheel. Despite her attempts to keep distance from Sun-jae, Sun-jae cannot help but be drawn to her. Eventually, he miraculously regains his memories and rushed to her for a heartfelt reunion.

With all memories back, Sol and Sun-jae escape their cursed fate and begin a happy relationship. Their story marks the end of a long, painful journey and the beginning of a new future together.