In Need Of A Good Anime To Watch Help Please.?

I am looking for a good anime to watch. I am really into dramatic stuff. So if there is an anime where the main girl turns evil I'd be interested. I sort of have an idea of what I would like to be in the anime too. My idea: so there was a couple and they got separated and the girl turns evil and the guy has to save her from dying or trying to kill everyone. I know it sounds like a lot to look for but I am really looking for something that fits that description. If anyone knows anything like

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