Guy, a man with the power to make couples have their best time together before one of them dies within seven days, receives weekly missions through the "Best Times" app. He arrives with a cold mist, but he can't predict which partner will die. Toey, a cooking studio owner, and Arm, an app creator, have grown distant despite once being a romantic couple. Toey becomes suspicious of Arm's loyalty when he forgets her birthday and seems too close to a woman named Prae. Guy enters Toey's life, claiming to be an old friend, and helps her navigate her relationship with Arm. After a serious accident, Toey learns from a fortuneteller that she's destined to die soon. As her life changes, she struggles with the truth and can't bring herself to tell Arm.