The Kōga Clan (甲賀) are a clan of fierce, made up breed of shinobi dogs, renown for their agile, speed, and strength.
The kanji in Ginga Densetsu Weed Meishōbu Retsuden of Tesshin's breed is 和犬の雑種 and stand for Dog of Japan (+mix). This is just what dogs in Japan were called before they were separated into breeds; the generic Japanese dog before classification (important note: although it's tempting to say it, 'original' dog is an incorrect term for this because it wasn't one breed that many stemmed from, it was a term for the group of dogs before they were separated into small [Shiba], medium [Shikoku], large [Akita] etc).
Yoshihiro Takahashi has later specified in an interview that they are a made up, ancient breed, most likely an offshoot of Kai dogs.
Kōga Ninjas were once allies of the Iga ninjas.
In 1579, however, they let down Iga Clan by teaming with Nobunaga Oda. When Nobukatsu Oda attacked Iga, Kōga Ninjas and their trained ninja dogs assisted him. Koga ninja dog named Sadamitsu fought with the Iga side, but he was killed.
The Kōgas are an ancient shinobi dog clan. They originally had human masters who eventually died out and the dogs were left alone in wilderness. They're mortal enemies of Akame and the other Iga shinobi dogs in their mission to steal ancient scrolls from the Iga dogs.
They're currently cannibalistic in nature from the order of their leader Kurojaki. Kurojaki believes that eating their opponents will make them stronger. There is about 40 Kōga dogs while Iga have less than 20 dogs.
The Kōga first appear when a one throws a piece of dog meat for a hungry Hyena. The Kōgas disappear when Gin and others show up. The Kōgas had been spying on the dogs for long and fled from the scene.
After this, four Kōga dogs face four Iga dogs and Gin. Two die in the suicide attacks commited by the Iga dogs and one is beaten by Gin. Gin also beats the fourth one, Maya. Gin and the Igas leave the scene, believing Maya to be dead, but he gets up and goes to tell Kurojaki what happened.
Because of this, the Kōga dogs are ready when Akame, Gin, Kirikaze and Jinnai come to take healing herbs from their territory. As the other invaders run, the Kōga dogs focus on killing the enemy leader. However, Akame is saved by Gin and Kurojaki loses his eye at the same moment.
Meanwhile, John has arrived the area, kills one Kōga dog and takes two of them as hostages. He rescues Hyena who was used as a slave by the two Kōga dogs, killing the two and also his hostages.
Kurojaki returns with his army and plans to beat John, but then the joined armies of Iga and Ōu show up to fight them as their final battle. Kurojaki's army loses the battle and he is defeated by Gin. Seven Kōga dogs join the Ōu army.
Kurojaki runs away and abandons his son after noticing fire - the Iga manor is on fire. Seeing the stealing of the secret scrolls inside the manor as his purpose of living, Kurojaki leaps into the flames despite Akame's try to talk him sense. The seven survived Kōga dogs soon follow their leader and jump into the fire. Akame respects Kurojaki and the other Kōga dogs as they died for their missions like true shinobis.
It's revealed that one of the seven Kōga dogs survived the fire and is now known as the Kōga Elder. He stays in Kōga to take care of the seven orphaned Kōga puppies and rises them to master shinobi techniques and to hate Iga and Ōu armies which ruined their ancient mission. The Elder also lets them believe that their fathers were killed by Iga and Ōu armies though they actually died in the fire.
Some months ago, Tesshin (son of deceased Kurojaki who was adopted by Ōu army) returned to Kōga. Sniper had lied to him that the Ōu army had beaten his father to death from Gin's order. The Elder gives Tesshin his rightful place as the ruler of Kōga Clan. The Elder wishes Tesshin would make their Clan great again but Tesshin only wishes to avenge the death of his father and doesn't wish to start war.
When Weed, son of Gin, arrives in Kōga territory to ask them to help fight the tyrant Hōgen, Tesshin fights him and his forces instead. However, Tesshin and his minions became allies of Ōu army after he finds out that the Ōu army didn't kill his father.
The Kōga dogs become valuable warriors for Ōu dogs. Other than fighting alongside with them to defeat Hougen, the Kōga dogs also worked as spies and messengers to Tesshin or Weed during the Russian Dog invasion at Hokkaidō.
In the anime, the Kōga dogs are kind from the start and have nothing against the Ōu army. Especially the Kōga Elder is completely different in personality and appearance.
The Kōga dogs live in a village instead of an underwater cave. They also have a notably darker fur color in the manga.
Most of the Kōga dogs survive the eruption of Futago Pass, but soon they hear of Masamune's conquest of Japan in place of the Ouu Army of the midst of it they lost their home to the Kurohabaki Clan while Tesshin recruits more dogs under the false name Jack to oppose the enemy clan. And continues their job as spies and messengers in the Ouu Army by stopping Masamune the Kōga dogs reclaimed their home.
Tesshin and the remaining Kōga dogs fight against Monsoon and his kin when the bears attack Paradise, after the army's defeat and escape, the Koga Elder dies of his injuries leaving Tesshin very distraught and in his haste to avenge his master the young Kōga recklessly attacked Monsoon but shielded by Tsukikage causing his demise. After Monsoon's and Sirius' deaths, Tesshin and Toshimitsu and all that remain of the Kōga clan.
- Ryōga - First known Kōga shinobi dog and the leader of the ninja dogs who fought in war against the Iga Clan.
- Izuna - Ryōga's son, he survives the war against the Iga Clan assuming the role of clan leader when his father passes away.
- Sadamitsu - One of the Koga ninja dogs and the only one that refused to betray Ōzaru and the Iga Clan but dies in the war.
- Resshi - One of the Kōga dogs following Ryōga.
- Juga - One of the Kōga dogs following Ryōga.
- Jirōta - One of the Kōga dogs following Ryōga.
- Kazumi - One of the Kōga dogs following Ryōga.
- Naojirō - One of the Kōga dogs following Ryōga.
- Take - One of the Kōga dogs following Ryōga.
- Tobi - One of the Kōga dogs following Ryōga.
- Kurojaki - Leader of the Kōga shinobi dogs and father of Tesshin. He was also the sworn enemy of Iga Clan's leader, Akame.
- Maya - Only named subordinate of Kurojaki.
- Tesshin - Son of Kurojaki and the current leader of the Kōga dogs. Nicknamed Chibi. He was raised by the Ōu Army.
- Kōga Elder - The oldest of 9 surviving Kōga dogs. Previously has a deep grudge against Gin, Weed and any Ōu Soldiers. Died from his wound.
- Toshimitsu - One of 7 Kōga dogs following Tesshin.
- Tsukikage - One of 7 Kōga dogs following Tesshin. Killed by Monsoon.
- Samu - One of 7 Kōga dogs following Tesshin. Dies from drowning.
- Shinbē - One of 7 Kōga dogs following Tesshin. Killed by the Bozlev's soldiers.
- White Tiger - Wolf that's a descendant of the Kōga.