As Naho Takamiya enters her second year of high school, she awakens feeling an unsettling sense of anxiety. To her surprise, she discovers a mysterious letter addressed to her from her future self a decade later. Initially doubtful, Naho soon realizes the truth of the letter's contents. It warns her to avoid repeating past mistakes and to make wise choices to prevent future regrets. The letter also cautions Naho about a transfer student, Kakeru Naruse, who will play a pivotal role in her life. Naho is told that she must tread carefully, or risk losing Kakeru when she needs him the most. With this newfound knowledge, Naho has the power to protect Kakeru and prevent future heartbreak.