The students of Class 3-E are tasked with a mission to kill a target before the world gets destroyed. That is all thrown away when the Reaper turns four Class E students into little kids!
Nagisa and Kayano are already boyfriend and girlfriend. Until a short time there's a big problem. Kayano broke up with Nagisa and Kayano is never to be found. After 6 months a new girl arrived named Saki Kahina and became Nagisa's close friend. And after for another 6 months, another new girl arrived named Ayano Yukik...