Few people are as unlucky as Tak Dong Kyung (Park Bo Young). A few years ago, her parents were killed in a sudden accident. Her reaction was to throw herself into her work as an editor of web novels. Her misfortune, however, strikes again when she is suddenly diagnosed with a brain tumor. One dark night, she climbs onto a rooftop and cries out to the heavens, begging for her suffering to end. This time, her plea is not left unanswered: her words summon a mysterious divine being named Myeol Mang (Seo In Guk), a go-between for humans and the celestial realms. He introduces himself, telling her he can grant her wishes if she is willing to pay the ultimate price. She agrees and strikes a fateful pact with him: she will be granted the life of her dreams for 100 days, after which the grim reaper will take her soul. However, as he gets to know this unique mortal better, Myeol Mang gradually begins to develop feelings for her… complicating the relationship between the human realm and the immortal realm.