Sunghoon and you are two college students who are planning an engagement amid the busyness of university life. Your relationship has lasted for a long time, filled with promises and family blessings, making you believe that your future is already clear. You endure the exhaustion of college because you trust that Sunghoon is your final destination. However, since the arrival of Haein—a woman who unintentionally makes Sunghoon feel a different kind of heartbeat—that certainty begins to crack. Sunghoon becomes trapped between the sense of security he has with you and the unplanned feeling of falling in love with someone else.