Outside Class 1-A, a mob of students, including Class 1-B, blocks the classroom's exit, and Tetsutetsu claims he came to see the class that fought against villains at the U.S.J., but only found a bunch of arrogant brats. Katsuki Bakugo ignores Tetsutetsu and walks away, prompting the latter to yell at him. When Katsuki gives the pledge to begin the U.A. Sports Festival, Tetsutetsu is angered by his arrogant claim to place first and promises to crush him.
During the Obstacle Race, Tetsutetsu uses his Steel Quirk to survive being crushed by a giant Zero-Point villain robot. He notices Eijiro Kirishima did the same using his Quirk and calls him a copycat. He and Eijiro battle throughout the course and Tetsutetsu ends up taking tenth place behind him.
For the Cavalry Battle, Tetsutetsu teams up with Juzo Honenuki, Yosetsu Awase, and Ibara Shiozaki. At the very start of the Cavalry Battle, Team Tetsutetsu goes after Team Midoriya for their ten million points. When they escape by using a jetpack to fly through the air, Tetsutetsu damns the support course. He later catches up to them and attacks again, but Team Mineta gets in the way and allows them to escape.
Despite being in second place until the final seconds of the round, Team Tetsutetsu fails to qualify after all their points are mysteriously stolen by Hitoshi Shinso. Confused, the team tries to explain what happened. Ibara says that it was karmic punishment for stealing Minoru Mineta's headband in such an underhanded way.
The finals are revealed to be a One-on-One Fighting Tournament, from which Mashirao Ojiro and Nirengeki Shoda decide to withdraw. Midnight has Team Kendo fill the empty slots, but Itsuka gives the opportunity to Team Tetsutetsu. Tetsutetsu happily thanks her as he and Ibara are chosen to compete amongst the top sixteen. He draws lots for matchups and ends up being paired against Eijiro.
Tetsutetsu congratulates Ibara after she defeats Denki Kaminari in the third duel and to fight in the seventh match. After trading hardened blow one after another, Tetsutetsu ends up fist fighting Eijiro to a draw. Midnight decides the winner of the contest will be decided via arm wrestling contest.
Once the last match of the first round ends the arm wrestling match commences. They both use their Quirks to try and gain an advantage, but Tetsutetsu's steel gives way and Eijiro pins his arm down to win and move on to the next round. Eijiro offers his hand to Tetsutetsu, congratulating him on a match well fought. Tetsutetsu shakes Eijiro's hand and thanks him for the compliment.
Eijiro advances to face Katsuki in the next round, and Tetsutetsu roots for him during the match. He constantly chants for Eijiro to go after his chin, and is disappointed in Eijiro after he is defeated. When Katsuki advances to the finals by defeating Fumikage Tokoyami, Tetsutetsu comments that the finals have been one big showcase for Class 1-A. Tetsutetsu joins his class during the closing ceremony of the Sports Festival to honor the winners.
Tetsutetsu receives a draft nomination from Pro Hero Fourth Kind to intern at his agency. When he arrives, he is surprised to see Eijiro there to intern as well. They happily greet each other and are introduced to the Chivalrous Hero himself. Fourth Kind explains that his agency was able to send out two nominations and he chose the two of them because he likes their guts. He goes on to explain how wages work for Pro Heroes, but Eijiro interrupts him, prompting Fourth Kind to yell at them both.
Sometime during their internship, Tetsutetsu and Eijiro fail to make tea to Fourth Kind's liking. He yells at them for making tea too sub-par for their clients and punches both of them in the head with their Quirks active. He comments on how satisfying it is to hit their Quirks. Following the incident in Hosu, Tokyo, Eijiro receives a message from Izuku Midoriya and tells Tetsutetsu it was a good thing he reported it. However, Tetsutetsu is afraid of being late to the agency and tells Eijiro to hurry up. Fourth Kind catches them being tardy and yells at them again. Before the internship ends, Fourth Kind takes Tetsutetsu and Eijiro to a local park to clean up.
Following the end of their first semester at U.A. High School, Class 1-B joins Class 1-A for training camp over summer break. When Class 1-B arrives at the training camp, their homeroom teacher Vlad King explains that they will be extending their Quirks and that the more they use their Quirks, the stronger they will be by breaking their limits. He also says that Class 1-B needs to join the spotlight, prompting Tetsutetsu to cry and apologize for disappointing him.
When the Vanguard Action Squad attacks the camp, the forest is filled with sleep-inducing gas. Tetsutetsu manages to avoid inhaling the gas thanks to a mask created by Momo Yaoyorozu from Class 1-A. He carries Ibara's unconscious body through the forest until he happens upon Itsuka, Yui Kodai, and Juzo Honenuki. He gives them masks to wear and entrusts Ibara's safety to Yui.
Itsuka tells Tetsutetsu they have to return to camp, but he refuses. Tetsutetsu believes Class 1-A is better only because they've survived crisis after crisis and used each one to grow stronger. Tetsutetsu resolves to fight the villains and prove that he can grow as well.
Mandalay eventually relays a message from Shota Aizawa granting permission for the students to fight back. As Tetsutetsu runs through the forest with Itsuka, he's excited to know he has permission to punch the villains. Itsuka stops him to explain that she's surmised that the gas hasn't dispersed to Mandalay's area because it's swirling around whoever is producing it with their Quirk. Tetsutetsu decides to charge straight for the thickest area of the gas in order to find the gas user. As they run through the toxic gas, Tetsutetsu says that he's angered by the actions of the villains because they hurt his classmates.
Tetsutetsu rushes through the gas until he finds the villain Mustard at its center. Mustard swiftly shoots Tetsutetsu's mask clean off his face. Tetsutetsu is uninjured thanks to his Quirk, but Mustard mocks him for his straightforward approach. The villain aims for Itsuka next. Tetsutetsu jumps in front of the bullet to protect her. Mustard kicks Tetsutetsu and shoots him repeatedly while mocking his personality, Quirk, and school.
Tetsutetsu begins to reach his limit in both Quirk usage and lung capacity. As his vision blurs, Itsuka attacks Mustard and thins the gas around them using her Quirk. Tetsutetsu capitalizes on this opening and punches Mustard with his steel enhanced fist.
Tetsutetsu's punch crushes Mustard's helmet and defeats the villain by knocking him unconscious. Victorious, the gas disperses and Tetsutetsu lies on the ground to regain his breath. Tetsutetsu claims the best way to beat a gas user who wears a mask is to destroy the mask and says the villains will pay for attacking the camp.
Itsuka and Tetsutetsu head back to the facility with Mustard in tow. After Katsuki Bakugo is captured, the Vanguard Action Squad withdraws from the battlefield, ending the attack. Mustard is arrested thanks to Itsuka and Tetsutetsu.
Following the Vanguard Action Squad Invasion, Nezu, Shota, and Sekijiro appear in U.A.'s public apology broadcast. During questioning, Nezu explains the most of the victims were harmed by Knockout Gas. Kendo and Tetsutetsu our recognized for ceasing the Villain producing the poisonous gas.
During the weeks leading up to the festival, Tetsutetsu is seen practicing for the theatrical performance of Class 1-B “Romeo, Juliet and the Prisoner of Azkaban: The Return of the Kings!”, where he plays the villain, Count Paris, Ghost of Azkaban.
Before the play, along with Neito Monoma and Yosetsu Awase, he visits Itsuka, who is preparing for the Beauty Contest she is forced to enter, and he’s impressed by Itsuka’s look. At the end of the performance, he goes to see the Beauty Contest with the rest of his classmates. After the contest, Tetsutetsu is seen hitting Neito, apparently for an unfortunate comment about Itsuka's defeat.
Tetsutetsu along with the rest of Class 1-B are pitted against Class 1-A as part of the Joint Training Battle. Shota Aizawa and Vlad King hold a competition between their classes during the early days of winter, with Hitoshi Shinso as a guest for this exercise, due being reviewed for consideration into the Hero Course. Vlad King and Shota begin the exercise immediately afterward. Each class chooses lots to split into five teams of four. He is placed in third round of match-ups, fighting alongside Juzo, Sen Kaibara and Pony Tsunotori; and they will face Class A's team of Tenya Iida, Shoto Todoroki, Mezo Shoji and Ojiro Mashirao at Round 3.
Before his match, Tetsutetsu encourages his classmates, being especially enthusiastic during the Round 2, where he supports and encourages Itsuka constantly during her battle against Momo Yaoyorozu.
During the transition to third round, Tetsutetsu admits to himself that he's not very bright however he knows that his 1-B team are at a disadvantage against class 1-A because none of them are particularly well suited for tracking down enemies or identifying their weaknesses, so he considers that the best option they have is to forego any strategy and challenges class A to a head-to-head fight. With this idea in mind, Tetsutetsu begins tearing through entire structures in his search for the other team. Pony and Sen disagree but Juzo's flexible attitude gets them to go along with Tetsutetsu's brashness.
Sudenly, Shoto blasts them with an ice attack, freezing all four of the Class 1-B students with a Giant Ice Wall. However, Juzo is able to free his team from Shoto's ice using his Softening Quirk. Freed from the ice, each member of the Tetsutetsu team faces a member of class 1-A, and he decides to take care of Shoto. Combining his Quirk with Pony's Horn Cannon, they destroys Shoto's ice defenses with their Horn Dash Hammer. Then Tetsutetsu grabs and throws Shoto to the ground.
Shoto tries to defend himself using freezing attacks but the iron fighter breaks through it with Tetsutetsu Fist. Tetsutetsu's iron body lets him break through the ice without ripping his skin. Since the ice barrage didn't work, Shoto tries burning Tetsutetsu with a Wall of Flames, but Tetsutetsu walks through the flames with his iron body glowing a bright red. He tells Shoto that his fire attacks won't work on him because he gained his heat resistance. He grabs Shoto to keep him in close range, with the idea of beating him until he falls unconscious.
Shoto brings out the heat from his body beyond its limit and creates a blaze hot enough that Tetsutetsu is forced to release him and backs off, as Shoto warns him to or else he'll melt. The flames begin to take a toll on Tetsutetsu, causing him to yell that it is hot. Tetsutetsu acknowledges that the heat is absurd and catches on to Shoto's plan to try and accumulate heat inside of him. However, he deduces that his opponent's plan is a double edge sword as raising the heat must also be taking a toll on himself as well and concludes that there is no way he can sustain that power for long.
He then proceeds to charge at Shoto with the latter blasting his flames at him and increasing its intensity. He knees Shoto and despite being warned he might melt, Tetsutetsu claims heroes have to risk their lives in practice if they want to last in the real field. Shoto simply tells Tetsutetsu he's too loud and continues to turn up the heat of his flames.
Tetsutetsu and Shoto continue to exceed their limits. Tetsutetsu yells that Shoto's flames have gotten weaker, while also yelling that it is hot. Shoto replies that Tetsutetsu has gotten slower as well. Shoto is about to perform an unknown Super Move when he is suddenly stopped by Juzo, who softens the ground with his Quirk. Juzo tells Tetsutetsu that he is going to melt and hardens the ground once again after debris falls on Shoto's head, leaving him unconscious.
Shoto slowly loses consciousness but Tenya swiftly rescues him by delivering a powerful kick on Juzo. He then carries Shoto and apologizes to him for being late. Tetsutetsu says that he won't let them get away, but he can hardly do anything. Juzo laments allowing Tenya to run freely and resolves to make up for his mistakes. Juzo refuses to let his team down due his mistake and in a last ditch effort, he softens a large metal tower before yelling to Tetsutetsu to push it over. The tower falls on Tenya before he can escape and get knocked out. At the same time, both Juzo and Tetsutetsu also collapse and are out cold.
Four competitors are down. Shoto, Tetsutetsu, and Juzo are all unconscious. Tenya's legs are trapped by the softened tower. Mezo chases Pony to Tenya's battlefield and Pony uses her horns to pick up all the unconscious players. She knows she can't carry Shoto to jail without Mezo stopping her. She refuses to lose for her team and levitates herself high above the field until time runs out. The twenty-minute time limit expires and the battle ends in a 1-1 draw.
Everyone is taken to Recovery Girl's office who heals everyone. Tetsutetsu chomping down on a Snickers bar offered by Recovery girl and gets Shoto attention and says he lost even though the match ended in a draw. He wants to have a rematch in the future and exits the office after commending Shoto's heart.
Afther this, Tetsutetsu watches the remainig rounds until the Joint Training Battle ends with a 1-A Class victory. Despite this, there are no hard feelings and that everyone is still friends with one another, and both classes hanging out together with no problem. Even though, Tetsutetsu scolds Eijiro for letting his defeat in the round 1 affect him and telling him to stop comparing himself with him. Tetsutetsu encourages a defeated Eijiro by telling him about the differences between Hardening and Steel and saying they both have different strengths.