 If you liked
Higurashi no Naku Koro ni Kai
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 ...then you might like
Shingeki no Kyojin Season 3
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These 2 are sequels to a series which have developed a deep mystery, but did not reveal a lot of answers. Finally, the answers are revealed (even if bot all in SNK s3 but a lot more than its prequels). There are too many secrets. I found them totally mind-blowing. It's interesting to see the characters make deductions and strategies. You might come to know that there were hints in the prequel but you missed them or things you thought to be less important turn out to be a key to solving the mystery.