Aiko Maebara

Maebara Aiko is a character in the Higurashi no Naku Koro ni series, and Maebara Keiichi's mother. She first appears in Onikakushi-hen along with her husband, Maebara Ichirou. She's rarely seen in the anime, but she appears various times throughout the manga adaptations. In the anime, it is a recurring habit that her face is not fully shown.

In Tatarigoroshi-hen, it's revealed by Keiichi that she's very fond of detective novels and reads all kind of crime novels of different writers all over the world (including books by Agatha Christie like And Then There Were None and Murder on the Orient Express). She also wrote a crime novel once and contributed to a crime novel contest. She easily reveals the trick of the perfect crime to Keiichi (not let the "introduction" begin) which helps him to murder Houjou Teppei. As it is told by Ooishi, she graduated in a "humble women's university".

(Source: Higurashi Wiki)