Chapters 1-30: Navier is a punching bag, the ML arrives. Everyone hopes that Sovieshu dies a dog's death, what an a***ole.
Chapter 30: Rashta's old slave owner blackmails her and she begins to participate in politics with a friend (?) advising.
Chapter 45 (ish) : Rashta becomes pregnant. It's made clear to her that the child will not be a part of the royal family, and she starts getting desperate. An attempt is made on her baby's life and people start really investigating her background.
Chapter 65 (ish) : Sovieshu figures out Rashta's secret and who tried to have the baby killed, and comes up with a very (very) stupid plan to legitimize it that involves divorcing his current wife, raising Rashta to become empress until she gives birth, and then marrying Navier again. Everyone hopes that Sovieshu dies a dog's death, what an a***ole.
Navier learns of the part of Sovieshu's plan where she's being divorced, triggering the actions that eventually lead to the scene in chapter 1, which I believe actually happens around chapter 80-something or so.
Surprisingly, I find myself really sympathizing with Rashta the more I learn about her. She's not a shallow white lotus villainness who does malicious things for petty reasons, but instead a character who behaves like what her background has molded her into. Habits that served her well as a slave don't do her much good as a concubine (aside from evoking pity). She doesn't mind using her body and beauty, which she probably learnt as a slave, but she has dreams of being loved and is starving for affection and attention. She's incredibly protective over her children and only really trusts herself with them. It's still unknown if she's hiding more malicious intents, but so far she seems to be more or less what she says she is.