Time to Say Thank You (chapter)

Time to Say Thank You (ありがとうの時間, Arigatō no jikan) is Extra Chapter 4 and the final extra chapter of the Assassination Classroom manga.

Short summary
Korosensei quickly contained the explosion, cleaned and repaired the property before Hotaru and the assassins could see it. Azusa is surprised by his speed. Korosensei admits that while surprise attacks can catch him off guard, he was fully prepared this time. Now in his teacher outfit, he revealed to Azusa that he had known she wanted to assassinate him simply from the bloodlust in her eyes, which he associated with one of his students. Azusa explained that she had contracted an unremovable infectious tumor that took away her eyesight and would eventually take away her mobility. With a lack of money and a large debt, she feared Hotaru would be destitute - until she overheard the assassins mention Korosensei's bounty. She concluded that as long as she made Hotaru some money, she would be able to survive. Korosensei complimented her plan, deducing that she would have blown herself up with Sengoku if he hadn't shown up.

Suddenly, Korosensei menacingly lifted up Azusa and quickly inserted a tentacle in her ear to remove her tumor to restore her eyesight; he explained that he had discovered it through observation as a result of his conviction to teaching. Before leaving for the classroom, Korosensei told that her life has value and she should spend it with Hotaru. From that point on, Korosensei never returned to the pub.

Back in the seven year timeskip, Nagisa is scolded by one of his students for taking a nap outside. Waking up to meet his delinquent students, Nagisa noted that even though he would make mistakes, he would do better and added that they were all growing up.

In a sequence after the author's afterword, a moping Kunudon was lectured by the spirit of Korosensei about how he could open himself to new possibilities if he would not give up; associating it with fish that thrived after adapting to changes in their environment. Kunudon turned around only to see a single cherry blossom, but decided that he would start things over.