X-DayX-Day.

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.