During high school, he labeled her a bully while she classified him as a jerk. Fate reunites Han-Eol and Da-Hae years later at their siblings' wedding. A tragic incident befalls the newlyweds, leaving their families pondering if they could have prevented the catastrophe. Suddenly, Han-Eol and Da-Hae awaken to a peculiar twist of fate—they are back in high school, and miraculously, their siblings are alive! Armed with just a diary and each other, they embark on a quest to alter their siblings' destinies. Will they succeed in reshaping fate, or is the outcome inevitable?