The story takes place in 21st Century Japan (approximately at the end of April 2010). The main character Nasu Souichi is a perfectly ordinary high school student, who tries to do as little as possible every day, and sleeps though most of his classes, only ever to be woken up by his friend Yuasa Satsuki. They believe they are living in a peaceful time, where no large wars are occurring.

However, these peaceful days are destroyed, when a number of large ships disappear at sea, almost instantly, and with no explanation as to why. A strange woman named Lisa＝Vixen suddenly appears and attacks Souichi... however Souichi also has his share of secrets.

[From Wikipedia]