Cha Dae Woong (Lee Seung Ki) is an immature and spoilt college student who comes from a rich family. He dreams of becoming an action star the level of Jackie Chan. During a visit in an old temple, he accidentally frees a Gumiho (Shin Min Ah) from a painting five centuries old. In his bid to escape her, he sustains a serious head injury. Miho takes pity on her saviour and shares her magical bead/energy to return the favour.
When Dae Woong finds out her true identity, he is terrified and tries to escape her but is met with a dilemma. In order to be fit enough to audition for a coveted action film, Dae Woong would need Miho's bead which then forces him to live with her. Miho, on the other hand, needs him to carry her bead for 100 days in order to be human. As they spend time together, they fall in love with neither knowing that in order for Miho to be human, Dae Woong would have to die.