Volume 18

Time for Valentine's Day (バレンタインの時間) is the eighteenth 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
Nagisa and Karma travel to the International Space Station in hopes of learning the secret to saving Koro Sensei’s life. Meanwhile, Yanagisawa and the upstart Grim Reaper II train ever harder to assassinate him. Then, when academic setbacks lower the spirits of his students, Koro Sensei comes up with an ingenious—or perhaps idiotic—way to cheer them up. Next, Valentine’s Day arrives! Will any of the 3-E students or teachers find true love? And will the meddling and teasing of the others help or hinder Cupid’s arrow in finding its target…?