My Forever Sunshine follows the turbulent life of Paeng, a young woman who loses her parents and is taken in by a wealthy family. After a traumatic incident where she attempts to seduce the family's son, Art, and subsequently causes a near-fatal accident, she is sent away to live abroad for several years. The story picks up when she returns home, hoping to reconcile with the family, only to find that Art still harbors deep resentment and bitterness toward her for the past. As they are forced to live under the same roof again, the tension between them is palpable. Art goes out of his way to make Paeng's life difficult, while Paeng struggles to prove that she has changed and seeks redemption. Through a series of emotional confrontations, shared secrets, and evolving circumstances, the two must navigate their complicated history to determine if their past wounds can truly heal or if their relationship is destined to remain in the shadows.