Based on the information given in the novel, as well as the plot of the female protagonist being called Jian Yan and the male protagonist being called Feng Qingchen, the novel I recommend is Parasite Me. The protagonist of the novel, Jian Yan, became the host of Feng Qingchen, who was parasitic in her body. The two of them began to rely on each other and rescue each other. I hope you like this fairy's recommendation. Muah ~😗