Tetsutetsu has hardened-like hair, metal-like eyelashes, and razor sharp teeth.
Tetsutetsu has a tendency to act hot headed and lets his emotions get the better of him, though he also isn't too stubborn to cheer for a rival, as he did so in Eijiro's match with Katsuki. Tetsutetsu is very determined to improve himself, as he apologized to his teacher for doing bad and vowed to do better. When villains attacked, he took the chance to expose himself to danger and grow from it. However, he also cares for his classmates, as he didn't face the villains before making sure that he left Ibara in the care of someone else.
Tetsutetsu is seen outside Class 1-A and says that he heard about them defeating villains and wanted to hear it directly for himself, but not from Katsuki, who he calls a snot nosed punk. He then yells that they better not embarrass them at the main event, which frightens Izuku, Tenya, and Ochako.
After Katsuki makes his declaration to place first, Tetsutetsu is angered by Katsuki's overconfidence and says that he will crush him. During the Obstacle Race, after Shouto causes the huge robots to tumble over with his Quirk, Tetsutetsu is buried alive by the robots, but he uses his Quirk to survive and dig himself out, saying that Class 1-A are a bunch of obnoxious brats. He eventually finishes the Obstacle Race and places 10th, allowing him to participate in the next event, the Human Cavalry Battle. He later teams up with Juzo, Ibara and Yousetsu.
Before the Human Cavalry Battle begins, Neito says to him that they should participate with no hard feelings towards each other, which Tetsutetsu agrees with. At the beginning of the event, Tetsutetsu's team attacks Izuku's team with Juzo using his Quirk to trap them, but Izuku uses his jet pack to escape. Tetsutetsu's team attacks them again, but Fumikage's Dark Shadow blocks them off. Tetsutetsu manages to evade Tsuyu's long tongue attack. After the Human Cavalry Battle ends, Tetsutetsu's team fails to qualify for the final event with Tetsutetsu confused as to how they lost all their points, with Ibara remarking that it is possibly punishment for taking the dwarfy kid's headband in such an unfair way.
After Mashirao and Shoda resign from the tournament event, Midnight says that the empty slots will be replaced by Team Kendo, but Team Kendo gives the opportunity to Team Tetsutetsu, much to Tetsutetsu's happiness. Therefore, Tetsutetsu and Ibara become part of the Top 16 in the tournament event and he is paired against Eijiro Kirishima in the first round.
Tetsutetsu faces Eijiro in his first round match. However, Tetsutetsu fist fights Eijiro to a draw, causing them to participate in an arm wrestling game to determine who will advance to the next round. After Katsuki defeats Ochako, Tetsutetsu faces Eijiro in their arm wrestling game to decide the tiebreaker. Tetsutetsu is defeated by Eijiro, which eliminates him from the tournament. Afterwards, Eijiro comments to Tetsutetsu that it was a fine match.
During the match between Eijiro and Katsuki, Tetsutetsu roots for Eijiro, telling him to hit Katsuki's jaw. After Katsuki defeats Eijiro, Tetsutetsu boos at Katsuki. After the match between Fumikage and Katsuki ends, Tetsutetsu notes that Class 1-A are hogging all the glory.
Tetsutetsu along with his class watches the closing ceremony of U.A.'s Sports Festival.
Tetsutetsu also goes out to gain workplace experience. Tetsutetsu's workplace of choice is revealed to be Force Kind's hero office. At the office, Force Kind explains to Tetsutetsu about his salary; that he receives it from the government. Suddenly, Tetsutetsu sees that Eijiro is in the office as well, surprising him. Tetsutetsu greets Kirishima with a hand shake. Force Kind decides to explain to them what his office's practical operations are.
When Class 1-B arrives at the training camp. Homeroom teacher Blood King explains they'll be extending their quirks and the more they use their quirks the stronger they'll be by breaking their limits. When Class 1-B witness Class 1-A's training. Afterwards Itsuka Kendo asks Shota Aizawa if can they observe everyone, he explains that's the reason The Pussy-Cats are around.
When the Vanguard Action Squad attacks, Tetsutetsu manages to avoid the poison gas thanks to a gas mask that was given to him by Momo. He also tells Itsuka that Awase is leading some of Class 1-A to the Class 1-B safe zone for aid. Tetsutetsu gives Itsuka, Yui, and Juzo masks. After Itsuka and Yui put their masks on and Yui puts a mask on the unconscious Juzo, Itsuka thinks that they should head back to the facility. However, Tetsutetsu refuses to flee and decides to stay and fight, telling Itsuka to take care of Ibara. Itsuka questions Tetsutetsu's actions, to which Tetsutetsu tells Itsuka why he has decided to fight; they have known for the longest time that Class 1-A has always been ahead of them because they have been exposed to danger and used that exposure to gain invaluable experience in order to become better Heroes. Tetsutetsu continues to say that they won’t be Heroes if they run away from evil and danger that threatens the lives of others. Tetsutetsu declares that he will expose himself to danger in order to become a Hero and promises to defeat the villains.
Tetsutetsu and Itsuka continue walking through the forest; Itsuka realizes that the gas is not dispersing and surmises that a villain is manipulating the gas; they decide to find the villain responsible for the gas. As Tetsutetsu and Itsuka reach the source of the poisonous gas, Mustard feels their presence and is impressed that they figured out the gas phenomena; he takes out a gun in preparation for their arrival. Suddenly, Tetsutetsu appears in front of Mustard and prepares to attack him with his steel fist. However, Mustard fires his gun at Tetsutetsu.
Tetsutetsu manages to block Mustard's bullet using his Quirk. Mustard shoots at Itsuka but Tetsutetsu throws himself in front of Itsuka to block the bullet. After Mustard attacks Tetsutetsu repeatedly, Itsuka attacks but Mustard evades; Itsuka enlarges her right hand and smacks Mustard away. Seeing that the gas is a hindrance, Itsuka enlarges her hands, uses them to swirl the gas away, and mocks Mustard for acting cowardly by using a gun to fight. Mustard prepares to fire his gun at Itsuka for her insult. Out of nowhere, Tetsutetsu appears behind Mustard, who was unable to notice Tetsutetsu's presence due to the gas dispersing courtesy of Itsuka. Tetsutetsu holds his breath and punches Mustard in the face with his steel fist, which crushes his mask and in the process knocks him unconscious. The victorious Tetsutetsu lies down on the ground and regains his breath.
Itsuka and Tetsutetsu head back to the facility with Mustard in tow. After Katsuki 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.
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.
Tetsutetsu appears to be on friendly terms with Neito, as he agreed to participating in the Human Cavalry Battle with no hard feelings towards each other.
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.
Both Tetsutetsu and Eijiro faced each other in the Sports Festival and fought to a draw. After Eijiro defeated Tetsutetsu in an arm-wrestling match and commented that it was a good battle, offering a hand shake, Tetsutetsu seems to have gained new found respect for Eijiro as he was cheering for him during his fight with Katsuki (although Tetsutetsu may have only cheered for Eijiro since he didn't want to see Katsuki, someone he despises, win). The two seem to have a heated, yet friendly, rivalry with one another due to their Quirks, abilities, and personalities.
- 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.
- 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 spinach.
- 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.
- (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!"