He is white Kishu Inu with a blue collar. He have brown eyes (sometime blue eyes).
In GDWO, he has burn scars around his face and body.
He admires Ohu soldiers, especially Weed, and is interested in the life of a wild dog.
He was once a little mischievous puppy, but even then his very brave and faithful to his comrades.
Kotetsu is very understanding when it comes to Weed's duties as the supreme leader of Ohu.
In GDWO, Kotetsu has grown up a bit as an uncle to Weed and Koyuki's kids. He is protective of them like when he tried to defend Rigel from the kai ken hunters.
Kotetsu, who was at the age of hyperactivity and rebellion, ran away looking to join the Ou Army, causing Koyuki to come looking for him. Koyuki however gets caught in a trap and Weed saves her.
Kotetsu meets the Ou army whilst they are eating and gives them a friendly greeting, but asks them to remember his name and face.
However, the group shun Kotetsu rudely for not being old enough to join, but is also given friendly advice from Cross to return home and wait until he is older and not throw away the happiness he has at home. Upset, Kotetsu is chased away by GB.
Koyuki tells Weed of Kotetsu and Weed, who has already developed feelings for Koyuki, tries to find him (Koyuki still has not developed feelings for Weed). But when Weed meets Kotetsu, he is being bullied by a group of older rogue dogs led by Yuusuke, who once belonged to Hougen's army.
The rogue dogs are eager to defeat their trespasser and they tear off most of Kotetsu's tail. Weed rescues Kotetsu scaring the pack of rogue dogs away and brings him back to his worried sister.
Kotestu reveals that Yuusuke killed his uncle Jirō, though it is not stated if it is his biological uncle or just an older dog he respected. That night, Kotetsu stays with Weed while Akame tends to his injury with a damp cloth. When Koyuki sees how Weed has saved her beloved brother, she begins to like him, visiting him more and more until they fall in love.
But when Weed has to leave for Hokkaido to save his father Gin, Koyuki, devastated, stays with Kotetsu hoping Weed will return soon. Koyuki and Kotetsu (who has developed feelings for Weed as an older brother) understand that Weed has certain duties as the Supreme Commander of Ohu.
When Viktor is defeated, Kotetsu is hunting with Koyuki when they come across a young puppy, Koshiro. Kotetsu calls for Weed when the puppy's pack turns up and is shocked when he learns that one of the dogs is Weed's older brother Joe.
Kotetsu doesn't fight against the bears but remains under protection whilst the fight goes on. After all the bears are defeated and Weed returns unharmed, Kotetsu and Koyuki rejoin the Ou army and Kotetsu becomes an uncle to Weed and Koyuki's children.
Kotetsu survives the volcanic disaster along with Gin's group and starts to work as a spy in the Kurohabaki Clan. He was also burnt and scarred by the fire.
Travel with Rigel
Upon the death of Terumune Kurohabaki, Kotetsu finds Rigel who ran away from other Kai Ken dogs. Kotetsu takes care of Rigel and together they travel to the town to find Daisuke, and Andy in a kennel. The two dogs go back into the mountains after hearing Gin and others are still alive, but encounter Masashige and fight with him. The fight stops when Masashige admits his actions were wrong and he is ashamed of them. Kotetsu allows him to follow them into the mountains, where they are attacked by more of the Kurohabaki clan. Masashige lets Kotetsu and Rigel escape as he fights off the dogs, only to be killed by them. His body is buried by Kotetsu and Rigel who go back to help him.
The Ōu Army
Later on, Gin and the others are freed from their captivity by Daisuke and Hidetoshi, and Kotetsu goes back with them to find Weed and the rest of the army. He is later reunited with his family and remains with the Ou army.
He also participates in the battle against Masamune and when he sees his nephew Orion tries to deal the evil clan leader the death blow but the pup is stopped by Weed. Then, watches with the rest of the army in shock as his brother in law banish Orion from Ohu and they all watch Masamune commit suicide.
Kotetsu is briefly seen with Weed after the attack by Monsoon, he stays with Gin for protection when the other bears invade. Since the attack, he has not been seen or mentioned but is presumed to be alive as his body has not been seen.
- Kotetsu and his half-sister Chako have the same mother, but a different father.