Kotetsu Hagane

is a chūnin-level shinobi from Konohagakure, and partners with Izumo Kamizuki.

Personality
Kotetsu is never seen without his partner, and best friend Izumo. He is characterised as being the more carefree and irresponsible of the duo, more willing to shirk his duties to hang out in the Jōnin Standby Station eating syrup for example. Similarly, Izumo admonished Kotetsu's lack of pride in his work when the latter complained that they were simply Tsunade's errand-boys. He is also described as being curious by nature, which was seen from the time he and Izumo disguised themselves as genin in order to see what type of people the new chūnin candidates were. Despite this, Kotetsu is a loyal and dutiful shinobi, with great love for his village and will carry out his missions despite complaining when they are trivial.

Appearance
Kotetsu has long, spiky, black hair and dark eyes. He has a strip of bandage running across the bridge of his nose and a light-coloured marking on his chin, although it has the same colour as his hair in the anime. He wears the standard attire of a Konoha shinobi complete with a forehead protector and a flak jacket. When deployed on missions, he usually carries a pair of bladed weapons strapped to his back.

Abilities
He is proficient with genjutsu as was seen during the Chūnin Exams in Part I, when he uses Demonic Illusion: False Surroundings Technique as part of an unofficial preliminary test of the new genin.

He is also proficient with weapons and armed combat, as seen in Part II, during his fight with Kakuzu, Kotetsu summons a large shell-like weapon from a scroll he was carrying. Since he was quickly captured by Kakuzu after this in the manga, it is unclear how skilled he is with it. However in the anime, it was shown to be able to perform aerial assaults. He also carries two large weapons with him which he and his partner Izumo wield with great proficiency often attacking from either side of the opponent. It was also shown that they can attach a chain to the hilt of these blades which they use to render their targets immobile before they attack them.

Chūnin Exam Arc
Izumo and Kotetsu first appeared disguised, trying to convince those planning to take part in the Chūnin Exams not to bother. Team 7 recognised that they had cast a genjutsu on the area, prompting them to give up in light of the group's skill. Seemingly somewhat impressed, Kotetsu attempts to attack Sasuke Uchiha with a kick, which Sasuke reciprocates in kind only to be stopped by Rock Lee. As they retreat and undo the transformation, he agrees with Izumo that the candidates this year seemed very interesting.

Later, Kotetsu and other chūnin arrive alongside Ibiki as invigilators of the first exam. Then, they sat on the outside of the examiners watching them for obvious sign of cheating, telling anyone who was caught five times that they had failed the examination. At one period in time during the exam, he threw a kunai onto the paper of a candidate that had failed, frightening Naruto as it had flown right past him.

He and Izumo were later seen together in the stands watching the preliminary matches. The two discussed Naruto's triumph over Neji and the talent that Shikamaru had shown in his battle, assuming he'd be an overall more suitable candidate than anyone else for promotion to the rank of chūnin.

Search for Tsunade Arc
When Tsunade became Hokage, Izumo and Kotetsu started doubling as her assistants and as guards to the front gates of the village. The anime indicates that they are easily ignored or duped by those using the Transformation Technique while on the job.

Sasuke Retrieval Arc
During Tsunade's transition into office he and Izumo Kamizuki became the assistants of Tsunade. They were the ones that found Sakura in the morning after Sasuke left Konohagakure and later informed Tsunade about the incident.

Pre-Shippūden Filler Arcs
Along with Izumo, he makes a few cameos in filler arcs. The first was the two of them carrying the chair Tsunade had kicked out of her office back to where it belongs. Izumo has a huge bleeding lump on his head as if he was the unfortunate recipient of the chair. The second is them guarding the entrance to Konohagakure, when the fake Naruto, Kiba, and Hinata enter the village. They express shock as the real Naruto and Kiba appear, as they had passed just minutes ago.

Kazekage Rescue Arc
In the anime, Kotetsu is seen with Izumo as Naruto and Jiraiya have returned after two and a half years of training. They are later seen at the village's gate as Team Guy and Team Kakashi are returning from saving Gaara from the Akatsuki.

Twelve Guardian Ninja Arc
Kotetsu is among the ninja defending Konohagakure from Furido and his team of ninja during the attempted siege on the village.

Hidan and Kakuzu Arc
Izumo and Kotetsu were assigned to a Nijū Shōtai team with Asuma Sarutobi and Shikamaru Nara, their mission being to find members of Akatsuki. They successfully managed to do just that. The team tracked an Akatsuki duo to a bounty station, where Izumo and Kotetsu stabbed Hidan during a sneak attack. When Hidan survived, they pulled back and were forced to watch Asuma fall prey to Hidan's jutsu, unable to help him. They instead engaged Hidan's partner, Kakuzu, but were easily captured and subsequently rescued by Raidō Namiashi and Aoba Yamashiro.

Upon returning to the village and debriefing, they inform Tsunade of Asuma's fate. Kotetsu along with Izumo are later seen attending the funeral, mourning the loss of their captain.

Invasion of Pain Arc
In the anime, Kotetsu is inserted as a member of the Konoha Barrier Team and is seen playing cards with other members when he hears about an intruder breaching the barrier.

Later, after Pain's invasion, he and Izumo were seen with Genma helping to rebuild the village. Kotetsu said that the Akatsuki had taken away everything that their forefathers had left for them.

Konoha History Arc
With himself as captain, he sent out on a mission to retrieve Condor from the Zeroth Training Ground with Naruto Uzumaki, Rock Lee, and Shino Aburame. During his battles with Condor, he experiences near death multiple times. Moments before his eminent death, his partner Izumo arrived to save him using their combination of Izumo’s Water Release: Starch Syrup Capturing Field technique and his own Conch Shell Mace to defeat Condor.

Shinobi World War Arc
After the defeat of the Gold and Silver Brothers, Izumo and Kotetsu launch a surprise assault on Kakuzu slashing him with their Kunai Blades and immobilises him by wrapping the chain attached to the blades around him. Kotetsu then says they came to repay him from their last encounter and ask Ino, Chōji, and Shikamaru to help them seal him. As the battle ensues, Shikaku contacts the two and informs them that he and Izumo, along with Darui were to deal with Kakuzu, while Team 10 would fight Asuma. Though initially protesting the orders because Izumo believed it to be too cruel to have Team 10 defeat their teacher, they are then seen chasing Kakuzu across the battlefield. He and Izumo are later seen standing over a defeated Kakuzu who was being restrained under Chōji's colossal fist.

Trivia

 * During Finally a clash! Jōnin vs. Genin!! Indiscriminate Grand Melee Tournament Meeting!!, Kotetsu engaged in a fight with Gaara, resulting in a humiliating defeat and a few broken bones after Gaara used Sand Waterfall Funeral on a weaker scale.
 * translates to steel and translates to iron.  is also similar to, which can also be translated as steel.
 * In the anime, it was shown that Kotetsu likes to eat pure syrup.
 * According to the databook(s):
 * His favourite foods are oden and tuna topped with grated nagaimo.
 * His least favourite food is bitter melon.
 * His desired opponent is Izumo Kamizuki.