In the vast land of Kyushu, the heavy tax of the imperial court forced fishermen to strangle their own children in order to make the mermaid cry and get the mermaid pearl. As a result, Haishi, a girl from a coastal fishing village, suffered from this. Her parents died and the whole village was slaughtered. At the critical moment of life and death, she sought help from Fang Zhu, the most powerful minister of Dazheng, who passed by here. After going through trials, she was finally taken back to Tianqi by Fang Zhu. From then on, Haishi disguised herself as a man and became Fang Zhu's apprentice. At this time, Dazheng was constantly troubled by internal and external troubles. The young emperor Chu Zhongxu, who was moody, lost all interest in life because of the civil strife in the dynasty. On the surface, he regarded himself as a tyrant, but when Fang Zhu struggled to support the peace of the country, he secretly watched all this. Haishi was ordered to become Dixu's guard, but this aroused Dixu's interest in her. The two experienced many life and death moments, from misunderstandings to gradually understanding each other. Dixu noticed Haishi's identity as a woman and secretly fell in love with her, but Haishi's dependence on Fang Zhu was full of hopeful but unspeakable feelings, and the emotional entanglement between the three continued. As the rebellion of the dynasty breaks out again, Hai Shi bravely chooses to shoulder the responsibility of protecting the peace of Da Zheng, and finally faces the feelings between Di Xu and Fang Zhu.