 If you liked
Gokukoku no Brynhildr
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 ...then you might like
Mahou Shoujo of the End
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Although not entirely similar in content, both series features dangerous girls that are considered a threat to society. They are ostracized as they are considered too dangerous.
Both series has a dark theme that is surrounded by mysteries regarding the origins of these girls.
Both series has horror themes as well as violence and gore. They also contain a plot that gets darker and darker as each chapter progresses. From the beginning chapter, the main male protagonist's life changes forever in both series.