Episode 37

Confession Time is the thirty-seventh episode of the Assassination Classroom anime and the fifteenth episode of Season 2. It premiered in Japan on April 22, 2016.

Summary
The battle between Kayano and Korosensei concludes with Nagisa using Irina's kissing technique on his friend and Korosensei removing her tentacles. As promised, Korosensei begins to tell his story of how he was the original Reaper and meeting Aguri Yukimura while in captivity by Shiro.

Plot
Kayano continues her ferocious attacks on Korosensei. It is immediately obvious to the class that the tentacles are consuming her mind, and Itona predicts that if nothing is done to prevent it she will truly die regardless of whether Korosensei is killed. At that moment, images of Korosensei's face sprout in front of the class while still defending himself. He states that the only way to save Kayano's life is to take away her tentacles, but unlike Itona's case, they do not have the time to calm her bloodlust. Hence he will need to remove them during their fight. It falls on the students to come up with a way to subdue Kayano for just a brief moment when Korosensei will intentionally expose his main weak point where Kayano will let down her guard. Kayano's next attack forces Korosensei to return his attention to her, as the students suggest various ways to do as they were asked. Nagisa thinks back to all the lessons they learned throughout the year. While most options are either ineffective or will result in Kayano being hurt, he suddenly remembers one particular technique.

Back to the fight, Korosensei exposes his crescent moon tie, prompting Kayano to strike his heart. However, her opponent catches her off-guard and restrains her with his arms. At that point, Nagisa approaches the struggling pair. Not believing everything Kayano had done with the class the past year was all an act, he calmly walks up to her and kisses her in the mouth. The whole class is shocked, but this manages to bring Kayano back to her senses before being unconscious after 15 "hits." Korosensei then surgically removes the tentacles from her neck.

With the battle over, the students crowd around Kayano. Rio Nakamura and Karma Akabane tease Nagisa about the kiss while Irina critiques that he still has much to improve on. Korosensei starts to recover from being hit in the heart but can still dodge an anti-sensei BB shot. The sniper is a hooded individual accompanied by Shiro, who is disappointed that for all of Kayano's talk about revenge, she was not capable of killing her target. Shiro removes his mask along with a device that alters his voice, and Korosensei recognizes him as Yanagisawa. Yanagisawa promises to kill him by March, and the pair leave the scene.

After Kayano wakes up, she tells the class that, at first, revenge was fueled by her pure bloodlust, but as she got to spend time with the class and Korosensei throughout the year, the more she began to think there was more to the circumstances that led by her sister being killed. Her weakening resolve, however, was not agreeable to her tentacles, and her bloodlust overwhelmed her, hence why she carried out her original plan. Nagisa comforts Kayano; stating that because of her he became comfortable with his long hair and that everyone agreed to her suggestion to name their teacher "Korosensei." Furthermore, the smiling warm girl they knew has long been accepted as their friend. Kayano weeps gladly as she no longer needs to put on a charade.

Isogai once again requests that Korosensei tell the truth about himself. He starts with what Karasuma and Irina had discussed during the summer vacation – the broader the knowledge of an assassin, the better you can teach. He puts this forward to the class and asks them why he is such an effective teacher despite this being his first year being so. Korosensei confirms that until two years ago, he was known as the Reaper. He went on to add that he would die in March, either at someone else's hands or when he explodes.

Korosensei then begins retelling his life. As a human boy growing up in a war-torn region, he only learned about death. As a result, he decided to become an assassin and honed his skills to kill people from intellectuals to powerful figures; in ten years, he earned the moniker of the Reaper. He was later taken captive and became a test subject to be experimented on by Yanagisawa, a researcher. The Reaper soon became acquainted with a female lab worker named Aguri Yukimura, whom he thought could be of use to him. He tries to get her to release him, but she refuses. He decided to bide his time, and covertly control the experiment so that he can use his new power to escape one day. While in captivity, he also witnessed Yanagisawa's cruelty to his fiancée.

In the next three months, the assassin and Yukimura become close, and she tells him she is a teacher at a school. In fact, she was somewhat awed that a professional assassin was schooling a high school teacher about quadratic equations. The assassin recounted how he was betrayed by his apprentice and could not understand where he made his mistake. Yukimura believes that his pupil wanted to be seen by him, something the assassin initially did not understand.

As time passes, the two grow closer; Yukimura asks the assassin about the exam questions she prepared, and the latter finally understands her meaning about wanting to be 'seen.' At this time, it was the beginning of the school year for the current Class 3-E, two weeks away from the creation of the permanent crescent moon.

Episode Notes
This episode marks the debut of the fourth and final opening, Bye Bye YESTERDAY.

Differences between Anime and Manga

 * In the manga Korosensei as a human, was seen attempting multiple times to escape with different methods, a couple of examples being manipulating some of the scientists or biting Yanagisawa. This does not happen in the anime.
 * The previous students of Class E were never shown in the anime.
 * The anime does not show ending a civil war as part of Korosensei's accomplishments.
 * Shiro's profile and position were never mentioned in the anime.

Trivia

 * The opening title has changed from "Assassination Classroom Second Season" to "Assassination Classroom Final Season."
 * Korosensei narrates the second half of the episode instead of Nagisa.