 If you liked
Denpa Onna to Seishun Otoko
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 ...then you might like
Classmate, Kamimura Yuuka wa Kou Itta.
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In both manga series, there is a strange girl who believes she is someone else and also develops strange ideas from her head. They think differently from other people.
Both series features a main male protagonist who is normal but get dragged into the strange bond between them. However, their bond becomes amusing as the series progresses and in a way that becomes closer and closer.
Both series has great artwork, a school life setting, drama, comedy, and even hints of romance here and there.