Volume 21

Time to say Thank you (ありがとうの時間) is the final 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 in their arsenal to combat Teach's alien technology, bizarre powers and...tentacles?''

Publisher's Summary
In the aftermath of tragedy, the students of 3-E nevertheless march proudly in their graduation ceremony. Will their futures still unfold as planned? And what will they do with their reward money…? Then, enjoy a long side story revealing what Koro Sensei was really up to over winter break! Can Koro Sensei truly make a friend and ally out of anyone…?! Plus, a bonus short story with all-new characters, set in a dystopian future.

Trivia

 * This volume has the most pages in it out of all the volumes by far.