On the day of Sera's wedding, Gaon helps Sera run away from the wedding and Jiho blames Gaon for it. A few days later, Sera visits a psychic and tells her that she wants to go back in time when Gaon and Sera were best friends. Sera asks Jiho to apologize to Gaon for yelling at her and plans for the three of them to meet up at a cafe. On their way to the cafe, all the lights suddenly go out. Gaon and Sera wake up to realize they have time-traveled to their senior year in high school. And it turns out that Jiho, Sera's fiancé, was in the same class.