Nina is the Saints sister, as we discover later on in the novel. There is a 5 year time skip before any romance even starts, so Nina is 19 once it starts.
After Nina is found out to be the saints sister, her status is upgraded from a maid, however she is not the saint now. Since her sister is still alive, but she will if something happens. So she’s more like help and the King likes that he feels cool when he touches Nina and starts to get attached to her.
It is speculated that Nina is the reincarnation of the first kings kill 1 to save 99 people lover. Which is why the King is more attracted to her since she is the reincarnation. Nina also is able to heal others, so she does that too. She gain a relationship with the Grand Duke(King’s younger brother)and the King gets jealous. That’s when she starts to realize her feelings for him.
However, there are side stories for people who weren’t satisfied with the King being ML. There is a side story for each love interest including Dio and the Grand Duke(forgot his name).
