"The Catastrophe of the Phoenix Ruins" fits the plot you described. The female protagonist is called Mo Xi, the divine beast is a phoenix, and the male protagonist is a dragon in his previous life. In the novel, the male protagonist's later state is indeed related to the coffin. This book was a fantasy romance novel with a complicated plot. If you like fantasy novels about interracial relationships, you can try reading them. I hope you like this fairy's recommendation. Muah ~😗