This volume begins with the story of Director Asano as a perfect teacher when he was young. An incident happened to one of his students which changes him to be a different person. This also explains the history of the main building and the Class E building. Later, Korosensei not only saves the Director's life but also confirms his ideal education system.
The Drama Festival is coming soon and Class E students already started to plan for the play despite they wish to focus more on their assassination work. What will be the story of their play which causes other students have lost their appetite and creates chaos after the play?
Another assassination attempt executed by Kayano and it appears Kayano is not her real name and surprisingly, she has tentacles as well. Her main purpose is to get revenge for her sister. After the assassination incident, the students are shocked and tried to recall their memories with Kayano and realized how little they know about their classmate.
In order to save Kayano from losing her life, Nagisa uses an unexpected assassination method to dissipate her bloodlust. What will be the unexpected technique which stunts everyone? A technique to cool her down and stops her from continuous attacking Korosensei but at the same time, she must not get hurt from it.
This volume ends with the beginning of the story of Korosensei's past which will be continued on the next volume.
More reviews can be found on Goodreads: Assassination Classroom, Vol. 15: Storm Time (Assassination Classroom #15).