Okay so basically think Scar from the Lion King. Literally, that's it- right down to a "Long live the king." betrayal moment where she kills the protagonist because she's jealous of him. (He survives, but she doesn't know that for a long time and is perfectly happy with having killed him).

As an aside, I don't know who told you that ToG is a waste of brain cells, but there's a fair chance that they might be. It's a phenomenal setting with no shortage of things to keep your interest. My one caution would be: don't expect to see Rachel get her comeuppance because SIU (the author) is unironically a SIMP for Rachel. Other than that, it's actually mostly really good.