You can say both of them are fl. It may seem like lady Medea is the main fl in the start but after chapter 30 you'll feel Psyche is also the fl. But Lady Medea is the main fl for me her story covers most of the plot.
You can think of it as two different stories with a fl for each. Both have completely different plot. Like if you see the story from Lady Medea's side you'll see one story of a girl struggling for power so she can live however she wants. Try to get out of the controlling parents.
And there's Psyche who gets to know the one she loves is a bastard (it's the crown Prince) who wants to kill her for the powers she possesses.
So, it's about their fight. (⌒▽⌒)
It's really good you should try it (=・ω・=)

Who is the main female lead? Is it the purple haired lady or the blonde? The reason I'm asking this is because I tend to like stories that has one female lead rather than two...