Nezu/Synopsis

History
Sometime before becoming U.A. High's principal, Nezu was experimented on by human beings. This mistreatment leads to Nezu developing a sadistic side to his otherwise polite personality. At some point he met Toshinori Yagi, knowing the secret of One For All, and made him a suggestion to look for a successor at U.A. and gave him the opportunity to look for a successor by taking up a teaching position at U.A.

Entrance Exam Arc
Nezu first appears among the judge's panel of U.A. faculty during the Entrance Exam's practical portion. He appears to be very excited when Izuku Midoriya destroys the gigantic villain bot in a single punch.

U.S.J. Arc
U.A. is stormed by reporters seeking information about All Might's teaching position. After the Police Force escorts the media off the property, Nezu and other teachers investigate the breach in the security barrier. They ponder whether a reporter was responsible or if a villain possibly penetrated their defenses. Nezu suggests that this was a possible declaration of war.

Nezu catches All Might trying to prematurely join Shota Aizawa and Thirteen as they instruct rescue training at the U.S.J. He lectures All Might about his proactive nature and how resolving criminal incidents has limited his ability to join the instruction. All Might asks to be excused so he can go to the U.S.J., but Nezu knows he would have to return almost immediately to conceal his identity and asks him to stay. Nezu pours them both cups of tea and begins monologuing about teaching philosophies.

Nezu joins his fellow faculty members as they follow Tenya Iida to the U.S.J. Following the assault on the U.S.J., Nezu is present for a meeting to discuss the attack and its implications regarding the league of villains and its leader, Tomura Shigaraki. Nezu suggests that Tomura is being guided towards villainy in the same way U.A. students are being guided towards heroism.

Final Exams Arc
Prior to Final Exams, Nezu holds a meeting with his faculty to discuss changing the format of the practical exam. He presents the idea that students should fight the teachers in teams of two in order to push them and make them as strong as possible. He also mentions that this is all in preparation of the rise of villains that's to come in the wake of Hero Killer Stain.

When the time comes to inform the students of the change, Nezu jumps out of Shota's scarf and takes upon himself to tell them the news. He explains that the recent surge of villains has caused the school to increase their training methods and from now on, U.A. students will take part in real life battle simulations starting with Class 1-A. He informs them all that the students will be tested by facing off against the teachers, shocking the students. Nezu is matched up against the pair of Mina Ashido and Denki Kaminari because their grades have been poor.

At the start of their battle in Ground Gamma, Nezu commandeers a crane with a wrecking ball attached to it. His Quirk gives him such high intelligence that he can predict the chain reactions of everything he destroys. This causes a lot of trouble for Denki and Mina, who struggle to find a path to the escape gate. Nezu drinks a cup of tea, noting that making decisions is rudimentary for him. He notices his opponents have not deduced his strategy and laughs maniacally at them from afar.

Denki and Mina try to run for the escape gate, but the principal stays one step ahead of them the entire time. He destroys all of their paths to the escape gate except for one. Even so, Denki and Mina run out of time before they ever even realize what Nezu was doing. They fail the test and prove their weakness lies in facing intellectual villains.

Hideout Raid Arc
After the League of Villains attacked the training camp, hospitalizing several students and kidnapping Bakugou and the Pussycat member Tomoko Shiretoko, Nezu, along with Shota Aizawa and Vlad King, appears in U.A.'s public apology broadcast where they apologize to society for their shortcomings. However, society still criticizes U.A. for being unable to protect the students and criticize their security measures for not ensuring the safety of the students.

Shota tells the reporters that he decided to let the students fight due to not knowing the full situation in order to prevent the worst possible situation from happening and as a result no students were killed (which is the worst possible outcome in his opinion); Nezu states that the situation would have been much worse if Tetsutetsu Tetsutetsu and Itsuka Kendo did not defeat the Sleeping gas villain. Nezu also says that they are seeing to the well-being of their students and have not seen any signs of emotional trauma.

The reporter asks the principal if U.A. had already failed in securing the students' well-being due to not checking Katsuki’s mental instability and his “villain-like” performance during the U.A. Sports Festival. Nezu, Vlad King, and Shota know that the reporter is purposely provoking them with this particular question. Shota answers that out of all the students, Katsuki was the one who showed that his conviction to be a Hero was the strongest and believes the villains to be foolish if they think that they can turn Katsuki into a villain. Nezu backs up Shota by saying that they are working with the Police Force to investigate Katsuki’s whereabouts and promises to retrieve him.

In the League of Villains hidehout, Shigaraki enjoys watching the criticism that the U.A. is suffering for their actions. However, Katsuki refuses to join their ranks and, encouraged by the words of his teacher Shota, rebels and trying to escape. At that moment, All Might, Shinrin Kamui, Edgeshot and Gran Torino assault the lair and quickly restrain the League of Villains'; Mr. Compress realizes that U.A.'s press conference was just a diversion so that the League of Villains' would lower their guard. It seems that the rescue operation has ended successfully, but All For One decides to intervene. Using the Quirk Warping, he teleports Bakugou and the League to his lair, while sending several Nomus to face the Heroes and the police forces.

Knowing where Bakugou and the others had been teleported, All Might quickly headed to the place after getting rid of the Nomus. Once there, thanks to Midoriya, Tenya and Eijiro, Bakugo is rescued, but All For One uses Warping again to allow the League to escape, leaving only him to face All Might, starting a battle between them that is televised to the whole country. Nezu, along with Vlad King and Shota Aizawa, watches the horrifying broadcast of All Might's bout. After an intense fight, All Might manages to defeat All For One, but consequently he loses One For All forever.

Several days later, All Might meets with Nezu alongside Vlad King and Eraser Head. Nezu thanks All Might for his victory against All For One as many lives were saved thanks to his intervention. Even though All Might will be continuing as a teacher, Nezu points out that since he is no longer able to fight, the parents of the U.A. students, as well as society, are anxious and worried about the safety of the children. Nezu reiterates that they must instill faith and confidence in heroes. Sekijiro Kan agrees with Nezu and vows to nurture, raise, and protect the students more strongly than before. Nezu decides that now is the time to implement a plan of his for quite some time. Nezu and Sekijiro will visit the parents of Class 1-B while Shota Aizawa and All Might will visit the parents of Class 1-A as part of the plan. The plan Nezu wants to implement is the transition of U.A. to a boarding school.