The League of Villains, led by Tomura Shigaraki, assaults the Unforeseen Simulation Joint with a large force of villain with the goal of killing All Might, attacking the students of Class 1-A in the process. With the help of his classmates, Tenya Iida manages to escape to call for backup.
Ectoplasm is one of the pro heroes who arrive at U.S.J with Tenya as reinforcements, arriving in time to save Class 1-A from the siege by the League of Villains. A group of villains attempts to attack them but Present Mic repels them with his Voice. Then Ectoplasm uses his Quirk to exhales a wave of ectoplasm that transforms into an army of Clones that beat the villains back and knock them.
Realizing that his plan had failed, Tomura managed to escape with the help of Kurogiri, despite the heroes' attempts to prevent it. With the leader of the villains on the run, the teachers scatter to defeat to defeat the remaining criminals and rescue the students. Ectoplasm takes down several more villains and rescues Denki Kaminari, Momo Yaoyorozu, and Kyoka Jiro.
Ectoplasm is present for the faculty meeting where the teachers agree to change the practical portion of the Final Exams. He is placed against Tsuyu Asui and Fumikage Tokoyami to take advantage of Fumikage's weakness at close range. He and the other teachers explain the changes to the exam to the students of Class 1-A.
Ectoplasm faces Fumikage and Tsuyu in the second battle inside a large labyrinth type building. Fumikage and Tsuyu start at the center of the structure and Ectoplasm spawns several of his clones around them. He warns them that he and the other teachers will do their best to crush the students. The students manage to flee into the upper levels of the building, but Ectoplasm keeps his clones in hot pursuit.Although Ectoplasm's clones manage to overwhelm Fumikage a few times, Tsuyu's support allows them to destroy twenty-eight of them. The students reach the vicinity of the escape gate where the real Ectoplasm is waiting. He compliments the tandem for defeating his clones but asks them if they can deal with his next attack. Ectoplasm uses Giant Bite Detention, a move that creates a giant clone of himself and traps the students inside it.
Immobilized, Fumikage orders Dark Shadow to escape in a last-ditch effort. Ectoplasm intercepts it and attacks with a flurry of kicks. Dark Shadow is unable to get past Ectoplasm with hand to hand combat and shortly retreats. They clash one final time, and Dark Shadow manages to handcuff Ectoplasm in a sneak attack. Tsuyu swallowed the handcuffs beforehand and gave them to Dark Shadow during its retreat. Having passed the exam, Ectoplasm releases the students from the giant clone and commends them on their clever synergy.
Ectoplasm, Midnight, and Cementoss join Shota Aizawa in his homeroom class to announce that Class 1-A needs to develop super moves.  They move to Gym Gamma, where Ectoplasm creates twenty clones for each student to fight in order to further develop their quirks and eventually create special techniques. This training is meant to prepare the students for the upcoming Provisional Hero License Exam. Ectoplasm uses Tenya's Recipro Burst as an example of a super move.
Ectoplasm easily defeats Mashirao Ojiro during a sparring match. He tells Mashirao he moves predictably and they need to work on his fighting fundamentals. Mina Ashido tries further the range of her acid attacks and Ectoplasm advises her to do so by forming her hands in the shape of a nozzle. Ectoplasm challenges Momo Yoayorozu to create two things at once with her Quirk, and she does so with ease. Katsuki Bakugo excels during the training and even manages to destroy one of Ectoplasm's clones before demanding he make another.
Ectoplasm catches Izuku Midoriya staring off into space and hits him. Izuku explains he's struggling to develop a technique because of the injuries to his arms. Ectoplasm agrees that Izuku's Quirk is too inconsistent and if he doesn't have a fixed fighting style than he needs to focus on developing it for the day. Ectoplasm also supervises Rikido as he eats sweets and tells Ochaco Uraraka to focus while levitating herself. 
Due to the incidents that have occurred in recent months, the Police Force's Commissioner General requests Nezu to cancel the U.A. School Festival, but the principal manages to convince him otherwise after assuring him that security measures will be increased. For this reason, Ectoplasm, Hound Dog and Snipe, Hound Dog are put in charge of security.
Shortly before the festival starts, Ectoplasm is informed that a student has left and has not returned, prompting Ectoplasm to look into the situation. However, Ectoplasm is soon informed by Hound Dog that there is a disturbance and requests to borrow five of Ectoplasm's clones, which Ectoplasm allows.
Upon reaching the place of origin of the disturbance, they meet Gentle Criminal and La Brava as Gentle declares his surrender. Ectoplasm recognizes Gentle from his online videos, and Hound Dog angrily asks him what their intentions are and what has happened. Soon after, Izuku arrives at the place and Izuku explains to the teachers that Gentle was trying to pull a prank on U.A and and they got into a small dispute but that everything is fine now.Hound dog is suspicious about his explanation, since both Izuku and Gentle are dirty and scratched, but reports that the festival to continue can continue without issue, and the teachers take Gentle and La Brava to the police station. After Gentle is escorted away, one of the Ectoplasm clones inform Izuku that All Might is worried about him and there is less than an hour left for Class 1-A's performance to start. Izuku panics after remembering he left his bag of items for the festival back in town and needs to get it and the Ectoplasm clone comes along with Izuku.
They get the stuffs back and return to the festival on time. The Ectoplasm clone suggests to Izuku that he cleans up his face before going on stage as his dirty face will worry the audience but he will still make it in time. In the end, the festival proceeds without incident. After Class 1-A performance, Ectoplasm sees All Might and Hound Dog scolding Izuku for his recklessness before letting him go to have fun at the festival.
The next after the Joint Training Battle between Class 1-A and Class 1-B, Ectoplasm and other teachers are in the meeting room discussing Hitoshi Shinso's transfer to the Hero Department. They decide that it will definitely be happening.
By the end of December, Ectoplasm is in the Conference Room with other U.A. teachers discussing the requests of the Hero Public Safety Commission. The Commission demand that all students from all hero high schools to undergo practical field training, restarting the Hero Work-Studies with the main goal the students learn how to cope the villain organizations that are beginning to rise.
By the end of March, thanks to the police investigations, and the information leaked by Hawks, who was acting as a spy, the Hero Public Safety Commission organize the Heroes and the Police Force to take down the Paranormal Liberation Front. Ectoplasm is part of the hero force led by Endeavor in charge of assaulting the Jaku General Hospital, where Nomus are created and where Tomura is hiding, and arresting its current board chairman, Dr. Kyudai Garaki, who is an ally of All For One.
When the raid begins, Ectoplasm is part of a team in charge of evacuating patients, medics and other civilians to a safe place, while another team faces the Nomu and reaches the underground secret lab. Unfortunately, Tomura awakens and uses his Decay to completely disintegrate the hospital, killing dozens of heroes in the process. It is unknown if Ectoplasm managed to escape in time.