Naruko Yokoshima (横島 ナルコ Yokoshima Naruko) is the most notable teacher in the series, easily making the most (of the few) appearances of any adult character. As a teacher, she is addressed as Yokoshima-Sensei (literally 'Teacher Yokoshima') by every other character.

Despite her role as a teacher and adviser of the Student Council, she is easily one of the most perverted characters in the series, probably even greater than either Shino Amakusa or Aria Shichijō.

The subject she teaches being English.

From the anime, "Seitokai Yakuindomo".