The person who took over FL's body knew she had to mate with ML so that was why she was ju...

The person who took over FL's body knew she had to mate with ML so that was why she was jumping on ML every chance she can get to try to seduce ML. ML got annoyed and hated her because of that. When FL returned to her body, he assumed FL was the same person as the one who took over her body. This novel has way too many dubcon/rape scenes that FL was forced to follow because of what appeared as a game system to her. Later on she finds out the game system is actually the god of their world forcing her to mate with ML because of some fate they have to fulfill. It's the same fate that the person who took over FL's body was trying to fulfill for FL. Basically, there's a prophecy that the child of FL and ML will start a whole new beginning in their world and considered a savior of their world, but FL and ML has to have sex for the child to be born, so the system/god forces quests and choices for FL to have sex with ML even when she didn't want to.

The plot is mostly FL trying to figure out what was going on because when she returned to her body, she has no idea why the game system still exists around her as she thought the other world was the game she had to complete. Later she realizes the game system was god following her throughout to make sure she fulfills the prophecy of giving birth to the future savior with ML. She also finds out that the person who took over her body wasn't someone unlikable and just someone who got unlucky with taking over her body and trying to fulfill the prophecy for her.

Towards the end, ML does change after realizing she wasn't like the other person and tries to be nicer to her, but she wasn't having it. He still pretty much forced his way into her life when he realizes she's pregnant with their child. The whole setting is pretty much forcing them to be together since FL was feeling sick when other people were around her. She only felt fine with ML around her because of their child in her womb. They end up together with her realizing somehow that she likes sex with him because she had always been a M since the beginning.

Story is written as a romcom so you'll need to be able to take this sort of humor to enjoy it. Otherwise, I can see a lot of people will hate their relationship because it is very coercive. When I was reading it, I didn't see S&M but more dubcon as FL couldn't control her body when the system was forcing choices on her. The author tried to make it light hearted with FL's views on calling their god a pervert many times. It also appears light hearted because FL has no trauma over the whole ordeal.