Higurashi When They Cry: Eye Opening Arc, Vol. 1 - manga

After a year at boarding school, Shion Sonozaki flees the oppressive institution and secretly returns to her hometown in the mountains, telling only her twin sister Mion of her arrival. Though the Sonozaki family has kept the sisters apart to prevent conflict over who would become the next family head, Mion and Shion have remained close - enough so that Shion can easily impersonate her identical twin. When Shion encounters Satoshi Hojo in town, he is completely taken in by her "Mion" disguise. And Shion is quite taken with him...