Eyi, the youngest daughter of the Dragon Emperor of the Heavenly Palace, was demoted to the mortal world for committing a serious crime to make up for her mistakes. By accident, she became the adopted daughter of Qing Boyan, the Dragon King of the Mortal Realm Well, and settled in the imperial city Qingjiao Well to hide her identity. Later, Qing Boyan became the prime minister of the dynasty, and Eyi became the prime minister's only daughter.
Eyi is an arrogant and unreasonable eldest lady during the day, and at night she becomes a demon-slayer dragon girl who makes demons frightened. The young prince Li Huan will never understand that she, who obviously knows nothing, can save him in danger time and time again.