Tetsutetsu is a young man with long gray hair that never appears to change shape, no eyebrows and thick pale eyelashes that encompass his eyes. Like Eijiro Kirishima, he also has razor-sharp teeth.
Tetsutetsu is defined by his very hot-headed and outspoken personality. He is confident, stubborn and very straightforward in both his motivations and his actions. He tends to be very vocal about his intentions and has a one-track mind. Tetsutetsu often looks for the simplest solution to problems in order to go about them in the most direct manner. Even when fighting, Tetsutetsu's direct personality shows through his tenacious and upfront fighting style.
Determined to prove himself, Tetsutetsu desires to be put on the same skill level as the students in Class 1-A. When Tetsutetsu first met Class 1-A, he was very loud and abrupt in his introduction because he felt they considered themselves superior to Class 1-A. He especially detested Katsuki for his arrogance and resolved to win the Sports Festival as a result.
Despite his stubbornness, Tetsutetsu eventually befriended Eijiro of Class 1-A and even cheered for him during the festival. Even so, Tetsutetsu continued to try and prove himself as a student on par with Class 1-A.
Following the end of the first term, the Class 1-B students were considered second-rate by everyone including their homeroom teacher. Tetsutetsu was brought to tears while apologizing for disappointing his teacher. When villains attacked both classes, Tetsutetsu fought back as an opportunity to expose himself to danger and grow from it. Much like Class 1-A did during the attack on the U.S.J.
Tetsutetsu appears to care deeply about his peers. He didn't attack the villains before ensuring Ibara Shiozaki's safety and didn't hesitate to throw himself in front of a bullet for Itsuka Kendo.
Tetsutetsu participates in the U.A. Entrance Exams and his efforts allow him to place eighth overall.
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 Hardening 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 fro 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, 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, and Juzo. 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 caputured, the Vanguard Action Squad withdraws from the battlefield, ending the attack. Mustard is arrested thanks to Itsuka and Tetsutetsu.
Quirk and Abilities
Steel (スティール Sutīru?): Tetsutetsu's Quirk allows him to turn his body into steel, which gives him a great defensive ability. He can also use it offensively to increase the strength of his unarmed attacks. Upon losing an arm wrestling match he mentions that he should have had more iron that morning, possibly implying that his quirk strength is fueled and affected by his diet containing iron.
- Eijiro Kirishima vs. Tetsutetsu Tetsutetsu: Draw, later lost on the arm wrestling contest.
Tetsutetsu despises Katsuki's arrogance. He has stated a desire to want to defeat Katsuki, but has not been presented with an opportunity to do so. When Eijiro fought Katsuki during the U.A. Sports Festival Finals, Tetsutetsu rooted for Eijiro to beat him.
Tetsutetsu and Neito appear to be on friendly terms, and can often be seen together. Although he didn't go along with Neito's plan to throw the qualifier in the U.A. Sports Festival, they agreed there would be no hard feelings in the Cavalry Battle.
Itsuka decided to let Tetsutetsu's team participate in the tournament event of the Sports Festival as her replacement, feeling that they deserved the opportunity more. They get along well as Tetsutetsu followed her deduction of villain being the cause of danger and they went after Mustard. When Tetsutetsu voiced that he will protect the class, Itsuka smiled and agreed with his declaration, showing she respects him.
Tetsutetsu also seems to value Itsuka's well being, as he rushed to her aid to give her a gas mask and protect her from the villains. The two appear to be on good terms, and unlike with Neito, the two have not been seen arguing or fighting or criticizing each other, indicating that their relationship is calmer than the one she has with Neito.
Tetsutetsu and Ibara appear to be close friends. The two teamed up in the Cavalry Battle and partnered up in the inter-class test of courage during the training camp. Tetsutetsu cares for Ibara's well being and made sure she was safe before he went to confront Mustard.
Tetsutetsu and Eijiro are constantly compared in the U.A. Sports Festival because of their Quirks, and eventually fight to a draw in the finals. This creates a fierce rivalry between the two that will not subside until Eijiro defeats Tetsutetsu in an arm wrestling match. Afterwards, Eijiro offers his hand and tells Tetsutetsu he put up a great fight. Tetsutetsu accepts the handshake and gains a new respect for Eijiro.
- His name is composed of the kanji for "iron" (鉄?), "clear" (哲?), "pierce" (徹?), and an archaic kanji for "iron" (鐵?). His name may be a joke mocking how similar he is to Eijiro Kirishima; his name sounds redundant, with each kanji being pronounced like the word for "iron" and he and his Quirk were formally introduced in quick succession and an identical situation to Eijiro. His name may also be referencing the Latin name for Tortoises (Tetsudinidae), as they are both known for being hard and resilient.
- Tetsutetsu ranked 8th during the Entrance Exam with 49 Villain Points and 10 Rescue Points.
- According to Tetsutetsu's profile in Volume 4:
- He likes fighting games.
- His favorite food is avocado.
- Kohei likes his design and wants to draw more of him.
- Tetsutetsu shares several similarities with Eijiro Kirishima.
- They share the same birthday (October 16).
- They both chose Fourth Kind's office for workplace experience.
- They share the same stats.
- Their Quirks, Steel and Hardening, are functionally similar and described likewise.
- Both have sharp teeth.
- In the anime, their Sports Festival entry poses were the exact same.
- Tetsutetsu ranked in the Top 16 of the U.A. Sports Festival First-Year Stage.
- Tetsutetsu also shares similarities to Gajeel Redfox from Fairy Tail, as both characters are voiced by David Wald in the English Dub, as well as using iron for their power.
- Tetsutetsu and his Quirk might be references to the Japanese cyberpunk horror film, Tetsuo:The Iron Man.
- His Quirk, Steel, is a reference to the DC Comics hero Citizen Steel , who's skin and muscle tissue are transmuted into organic steel. It might, however, be a reference to the Marvel Comics hero Colossus, who can transform his skin to organic metal at will.
- (To Itsuka Kendo) "I'm in Class 1-B of the Hero Course! If I don't stand up here, what's the point?! I'm gonna find these jerks and beat the snot out of them!"