A Thousand Days' Promise

Ji Hyung, a betrothed man, is having a decade-long affair with Seo Yeon, a writer with a haunted past.

After meeting Ji-hyung, Jae-min becomes worried about Seo-yeon and tries to console her. Meanwhile, Hyang-gi sneaks into Ji-hyung's room. In his sleep, Ji-hyung accepts Hyang-gi's presence unknowingly.

Seo Yeon's visit to the hospital leads to a devastating diagnosis; Ji Hyung feels increasingly distanced from his fiance.

Seo Yeon asks Moon Kwon to quit his part-time job; Moon Kwon and Jae Min begin to suspect something's wrong with Seo Yeon's mind.

Ji-hyung seeks out Jae-min to find out about Seo-yeon's disease. Soo-jung, Ji-hyung's mother, asks if Ji-hyung is capable of letting Seo-yeon go. Later, Ji-hyung decides to confront Seo-yeon about her disease.

Ji-hyung reveals his affair to Hyang-gi and breaks off his engagement. Hyun-ah, Hyang-gi's mother, becomes furious at Hyang-gi's attempt to defend Ji-hyung. Meanwhile, Seo-yeon struggles to cling onto her memory.