The premise of the anime without the reincarnator has too many plot holes. If Slow loved her, why did her treat her badly? If Charlotte started to love Shuya just because he saved her once, what about all the times that Slow protected her? He protected her from the shadows, but it was also shown that he did it in front of her too. If it was because Slow was unattractive, why would Slow go out of his way to make him look unattractive? Becoming fat isn't a necessary point for him to be disowned by his family. I also don't see why the people that watched the anime would like Charlotte. She discarded Slow for a random dude(from her perspective) that saved her once. When compared to how people IRL behave towards that kind of development, that would only give reasons for them to dislike her, some would even hate.