Catgirl Syndrome (Katorusu Syndrome) is an unexplained illness primarily affecting girls aged 0 to 12, who suddenly undergo 'catgirl transformation.' There are two things that modern medicine has clarified. One is that they are 'cute.' The other is… 'they get butterflies when they see girls.' (Author: Nekotarou / First published: GANMA! Episodes 29-38)