About a female college student named Lee Dam who accidentally swallows the marble of a male gumiho (a mythological nine-tailed fox) named Shin Woo Yeo, who was close to achieving his goal of becoming human. If a human swallows the marble, they can only live for one year, and the marble will break, preventing the gumiho from becoming human. Thus, Shin Woo Yeo suggests living together to Lee Dam, beginning their unexpected romance.

Shin Woo Yeo is a gumiho with good looks, sturdy physique, good manners, and a sweet charm who has lived for 999 years.

Lee Dam is a college student who doesn’t hesitate to speak the truth. She is a firm, straightforward person who is very self-objective, which may be the reason she has never been in a relationship before.

Yang Hye Sun is a female gumiho who has an innocent heart despite her stunning good looks. (In traditional folktales, gumiho were usually beautiful women who seduced men to their deaths.) She is Shin Woo Yeo’s friend and a former gumiho who achieved her dream of becoming a human. Although she seems perfect on the outside, she is actually rather clumsy and naive. Do Jae Jin is a fool when it comes to love. When he falls in love, he’s ready to give up everything, including his life and organs. He is Lee Dam’s close friend. Despite his good looks, good physique, and good personality, he is unable to find true love. He ends up falling in love with Yang Hye Sun, the former gumiho.

Gye Sun Woo is Lee Dam’s college senior who has an unrequited crush on her. He is extremely popular with women at their college, coming from a good background with both brains and beauty. But after Lee Dam firmly turns him down, he finds himself experiencing unrequited love for the first time in his life.

Adapted from a webtoon of the same name by Na.