"A Thousand Days' Promise" tells the story of a woman losing her memory and a man who loves her unconditionally. Lee Seo-Yeon (Soo-Ae) and Park Ji-Hyung (Kim Rae-Won) have known each other since they were teenagers. Lee Seo-Yeon lost her father when she was only 5-years-old and her mom left her when she was 6. Seo-Yeon was left behind with her younger brother Moon-Gwon. Her aunt took them in and raised in her home.