Strong Female Leads

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She reincarnates into the body of the FL of a strictly romance novel. Even though she follows the story line as closely as possible on the day of the confession the story genre changes and there is a zombie apocalypse
Every time the MC is killed she goes back in time to the morning of.

The MC is reincarnated into the villainess instead of trying to survive she wants to die.
The MC believes that if she dies she will be able to return to her world - the only problem is due to the novels laws she can't kill herself
I found this story pretty sad so far because the MC and the OG villainess both experienced unnecessary suffering.
There are quite a few plot twists and the ending may not be what you expect

Contract Marriage Trope
The MC was reincarnated into the villainesses body after making a deal with the devil. If she can fulfill the villainesses wish in the 6 months she has left to live he will revive the MC in her world.
Clea's circumstances are stacked against her because her body is super weak lol. The ML is very doting as well

The villainess leaves the capital to live in one of her families territories. She finds it cold so she summons a demon to light a fire and now she's stuck with him.
The dynamic and skinship between the ML and FL is super natural and wholesome. There are a bunch of comedic moments as well. The FL is pretty OP in the sense that she gets a bunch of allies and powerups with minimal effort (most of the time it's accidental lol)

Free on Webtoon
After being betrayed by her first love she decides to become empress of her kingdom and exact revenge... By getting a harem of her own
She's calm, calculating, and strong. She doesn't act like a weak or submissive person and does what has to be done. There is definitely a variety of personalities being introduced into her harem so depending on what type of ML you like there will be one for you
Same author as 'Remarried Empress' but this one is much more fast