Kotetsu Hagane

is a Chunin from Konohagakure. He spends most of the time with his partner Izumo Kamizuki watching who enters and leaves at Konohagakure's Main Gate. Many times, most of the time during the Filler arcs, they are easily fooled with Transformation Technique or ignored by people who run past the gate.

Chunin Exam arc
During the Chunin Exam's first test, he was sent to test the Genin by casting a Genjutsu, which made the Genin see the second floor as the third while using Transformation Technique to look like a kid. While in this form, he tried to pick up a fight with Sasuke Uchiha but Rock Lee stops both their kicks. Later on the third test, Kotetsu and his friend Izumo Kamizuki watched over the Chunin exam, giving feedback on the Genin's qualities.

Search for Tsunade arc
After Tsunade became Hokage, Izumo and Kotetsu served as her assistants, and Kotetsu called Tsunade as "a real slavedriver".

Sasuke Retrieval arc
At the beginning of the Sasuke Retrieval arc, they are the ones who wake up both Sakura Haruno and the Fifth Hokage. The latter sends them to get Shikamaru, who is given his first mission as a Chunin: to lead the Sasuke Retrieval Squad and bring Sasuke back.

Part II
After the timeskip Kotetsu and Izumo were the first to know of Naruto's return, since they were watching over the gate.

Hidan and Kakuzu arc
After the news of a team consisting of 2 members of Akatsuki was infiltrating the Land of Fire reached the Fifth Hokage, Konohagakure decided to form the Niju Shotai to track them. Kotetsu, Izumo, Shikamaru and Asuma served as one of the 20 teams to track down the Akatsuki pair, Hidan and Kakuzu. They arrived to the Fire Temple to find it decimated and most of the monks dead. After noticing that the Head Monk's body,Chiriku's, was missing, Izumo noted that it had a high value in the black market, so the team went to the nearest exchange point to intercept Hidan and Kakuzu, engaging in fight with them. Despite stabbing Hidan in his vital organs, the team learned too late that both Akatsukis were immortal, and the team's leader and only Jonin, Asuma, was killed. They were shortly after assisted and saved by Raido Namiashi and Aoba Yamashiro, but the fight was interrupted by the Akatsuki Leader calling back, telepathically, Hidan and Kakuzu.

Abilities
The abilities Kotetsu has shown us so far throughout the anime and manga are genjutsu, having made the 2nd floor of the Academy appear like it was the third. During the fight against Kakuzu, he used Summoning: Conch Shell Mace in an attempt to defeat him, but Kakuzu was able to counter the attack thanks to his tentacles. Kotetsu also wields two large kunai knives, which he can use together with Izumo for attack.

The Bandage
Since Kotetsu uses the normal Chunin uniform (the Flak Jacket), his most representative trait is the bandage he wears across his face, over the nose. At one point, Asuma, Izumo and Shikamaru ask him about this and remind him that he didn't use it when he was a kid (back when he was using transformation technique to disguise his appearance). As with Kakashi's mask, a lot is in question regarding what's below the bandage, be it a horizontal line of pimples or freckles or even long whiskers. Later he agrees to take the bandage off but then Shikamaru states that knowing it would only be troublesome much to Kotetsu's chagrin, so the reason for the bandage over the nose remains unknown.

Trivia

 * During the Naruto Ova that came as a bonus for Naruto: Ultimate Ninja 3, Kotetsu engages in fight with Gaara, resulting in a humiliating defeat and a few broken bones.