Tetsutetsu is a young man with gray hair, no eyebrows and thick pale eyelashes that encompass his eyes. Like Eijiro Kirishima, he also has razor sharp teeth.
Tetsutetsu has a tendency to act hot headed and lets his emotions get the better of him, though he also is not 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 Tetsutetsu first appears outside Class 1-A in a mob blocking the classrooms exit. 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. A member of Class 1-A, 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. 
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's headband in such an underhanded way.
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 thier ten million points. When they escape by using a jet pack 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. 
The finals are revealed to be a One on One Fighting Tournament that Mashirao Ojiro and Nirengeki Shodadecide to withdraw from. 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.</span> 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 iron 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's 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 also goes out to gain workplace experience. Tetsutetsu's workplace of choice is revealed to be Fourth Kind's hero office. At the office, Fourth 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. Fourth 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 Pussycats 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 Yaoyorozu. 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 will not 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 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.
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.
- Both their Hero names contain alliteration.
- 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!"