In order to cure his younger sister Xiaopiao, Liu Yidao, who is known as the “Monster Killer” in the world of martial arts, retired to have more time to find famous doctors. The demon clan, led by Toad Demon and Serpent Spirit, tried to revive Black Dragon to rule the whole world. They constantly made trouble in the human world to improve their own cultivation. Xiaoluan the Koi carp mistakenly got in the human world and was caught by the Man-monster Pavilion. Liu Yidao rescued her in order to get paid, and later he learned that Xiaoluan was the reincarnation of the Black Dragon. At the time, the monsters also learned the true identity of Xiaoluan, and wanted to take her to summon the Black Dragon. During the time Liu Yidao was protecting Xiaoluan, they fell in love with each other.