X-Day (Japanese: 彼女達のエクス・デイ, Hepburn: Kanojo-tachi no Ekusu-Dei, lit. "Their X-Day" or "The Girls' X-Day") is a Japanese manga series written and illustrated by Setona Mizushiro. It was serialized in Princess magazine from March to November 2002 and published in two tankōbon volumes by Akita Shoten. Written in response to the Columbine High School massacre, the story follows three high school students and a teacher who meet online and plot to blow up their school. Source: Wikipedia (en)