I'm not sure specifically as I haven't read it. It might be about the life of an imperial consort, perhaps her rise to power, her relationships in the imperial court, and the challenges she faces in that complex environment.
I don't know the exact main characters as I'm not familiar with this novel. But it's likely that the imperial consort herself is a main character. There may also be the emperor and perhaps some court ladies or eunuchs who play important roles.