Yejin and Haeri are the best friends in their class. But when Haeri starts writing a secret diary with friends from another class, a subtle crack begins to form in their relationship. Yejin feels hurt by the way Haeri keeps the diary from her and grows anxious, wondering if their shared secrets might have been written inside.

Seok-young, a girl who loves to swim, comes to the countryside and bumps into mysterious Woo-ju. They get closer after Woo-ju saves her from drowning. However, they part ways when Woo-ju leaves the countryside to pursue his dream. Woo-ju is now a promising swimmer, and Seok-yeong cheers him on from afar. Will they ever be reunited as they swim between feelings of inferiority and puppy love?

Ji-soo, a literature enthusiast who believes a mysterious being once visited him as a child and gifted him with talent in writing, finds school life boring. But everything changes when Hyeon-joo, a bold, soccer-loving girl, transfers to his school. Her boyish charm and passion to soccer instantly captivates him. From that day on, Ji-soo is plagued by unsettling, yet vivid dreams that blur the line between reality and something far more mysterious.

Yeong-ju lost a friend because of the 'Seoul Halloween crowd crush' in 2022. Unable to recover from the trauma, she took a leave of absence from college and volunteered to give career counselling to middle school students while undergoing psychiatric treatment. As time passed and both her treatment and volunteer work came to an end, the traumatic autumn came around again.