In a Kingdom where a Prince can only be the Emperor and rule the kingdom if he finds his significant other, the dying Emperor Yi Xing calls his son, Prince Lu Han to find a suitable partner for himself. The Palace orders the whole Kingdom for each of the family to send one girl of age fourteen to eighteen to join the Princess Selection, and the family that won't send their daughter would be killed.

The Oh Family, only having one daughter, Sena, has cancer and only has 3 months left to live. Wanting to enjoy her last days, she asks the only person in the household that cares for her which is her brother, Sehun.

In order to save his family from the Kingdom's punishment, Sehun finds himself joining the Princess Selection, disguising as her sister, Sena.