Catgirl Syndrome (Katorusu Syndrome) is an unexplained illness that primarily affects girls aged 0 to 12, causing them to suddenly transform into 'catgirls.' There are two things that modern medicine has clarified about this condition. One is that they are 'cute.' The other is... that they 'get excited about girls.' (Author: Nekotarou / First published in: GANMA! Episodes 39-51)