Episode 38

Past Time is the thirty-eighth episode of the Assassination Classroom anime and the sixteenth episode of Season 2. It premiered in Japan on April 28, 2016.

Summary
The captive assassin and Aguri Yukimura continue to bond over their time conversing with each other. On the anniversary of their first meeting (March 13), the crescent moon came to be as a direct cause of Yanagisawa's anti-matter research. To avoid Earth meeting a similar fate in one year's time, Yanagisawa prepares to kill the assassin but the latter turns into a tentacled monster to escape the lab. However Aguri is killed by a hidden mine, and the assassin promises to carry on teaching her students for the remainder of his life. After Korosensei finishes his story, the class realise the heavy burden that is placed on them to kill their teacher.

Manga and Anime Differences

 * When human Korosensei started to mutate, he doesn't have any self-destruct device inside him while in the manga he pukes out the self-destruct device that was installed in human Korosensei.
 * During his rampage, the room was less spacious as he engages Yanagisawa's soldiers on the hallway while in the manga he rampages in the library.
 * This also happens when the tentacle mine was triggered; it was on the side of the room rather than hidden inside the floor.
 * The defense and soldiers that was set up by Yanagisawa was more heavier for the armed soldiers but more lighter on the defense barricade itself compared to the manga.
 * Yanagisawa already set up anti-tentacle material fences but the soldiers are less armored while in the anime the soldiers were more armored while the fences were made of fiber glass.
 * The damage that took Yanagisawa's eye was different from the manga itself. In the anime he took damage from a tube while in the manga he took damage from the shards of table that destroys the anti-tentacle fences.
 * When the last term of semester begins, Korosensei meets them at the classroom while in the manga he met them at the front of the school itself.

Trivia

 * The opening song Bye Bye Yesterday is not featured in this episode, instead only showing the title card.