Isabel, a terminally ill orphan in modern-day Korea, unexpectedly finds herself reincarnated as Princess Isabel in the world of the novel "After the Terminally Ill Villainess Dies". While she still carries the curse of the "Mark of Narvidal" and is destined to die at 21, Isabel embraces her new life with joy, determined to make the most of her remaining time. However, being born a girl in the Bilotian Empire, where strength is paramount, is a curse. Despite facing prejudice and initial coldness from her father, Emperor Ron, Isabel's precociousness and surprising strength win over her nanny and the Emperor's aide, Sir Viaton. Her innate magical talent, revealed through her "Innate Chant" and keen observation skills, attracts the attention of Karin, the future final villain of the novel, who becomes her magic teacher. Isabel navigates the complexities of palace life, charming her stoic father, forging an unlikely friendship with her playful but clueless brother, Michael, and winning over the stern Chief Attendant Dailtha. She uses her knowledge from her past life to excel in magic and even creates groundbreaking theories, inadvertently impacting the future of magic engineering. Despite her terminal illness, Isabel focuses on spreading happiness and leaving a positive impact on the world. She befriends a honey badger, later revealed to be the transformed male lead Arun, and rescues a talented young girl, Yuri, from the clutches of the jealous and manipulative Reina, daughter of Duke Rossild. As Isabel grows, she faces the challenges of her limited time, the complexities of palace politics, and the looming threat of the final villain, all while spreading kindness and warmth like sunshine. Her journey is a testament to the power of embracing life, even in the face of death, and the impact of even small acts of kindness.