Volume 16

Past Time (過去の時間) is the sixteenth volume of the Assassination Classroom manga.

Preface
''Ever caught yourself screaming, "I could just kill that teacher"? What would it take to justify such antisocial behavior and weeks of detention? Especially if he's the best teacher you've ever had? Giving you an "F" on a quiz? Mispronouncing your name during roll call...again? How about blowing up the moon and threatening to do the same to Mother Earth—unless you take him out first?! Plus a reward of a cool 100 million from the Ministry of Defense! Okay, now that you're committed... How are you going to pull this off? What does your pathetic class of misfits have at their disposal to combat Teach's alien technology, bizarre powers and...tentacles?!''

Publisher's Summary
Koro Sensei tells all: his former profession, his nickname, the mad scientists responsible for his unique cephalopod physiognomy, the love of his life, and why he wants to teach the 3-E students. New light is shed not only on his character, but on the reason he vowed to destroy the Earth in March. Will these revelations change 3-E’s commitment to assassinating their teacher (and saving the planet)?