Moss was an enormous Mastiff, mentioned to be two times bigger than Ben.
He was several times mentioned to be very fat, but he also had very powerful muscles. He had many scars all over his body.
He wore a brown collar (greenish-spiked in the anime) around his neck, revealing that he was once a pet. Moss was the biggest dog in Ginga Nagareboshi Gin while the biggest wolf is Mukonga.
In Ginga Densetsu Weed, his collar was missing.
Moss was an impatient and a bit short-tempered dog. He might get scary when angry, with an appearance like that. He didn't listen to rational talk while being overwhelmed by emotions.
However, he had soft spot for puppies, even so that he tended to spoil them. He was very gentle towards pups and got furious if an adult dog hurt a pup. His son, Jaguar was very dear for him and he became violently furious when he thought that he died.
Moss disliked the Kai Brothers, though he admitted to Jaguar that he didn't really hate them and had certain respect towards them (he even planned to make them his heirs). He later accepted them as his comrades and started to have comical quarrels with Smith instead.
It's implied that he loved to eat, explaining his heavy build. He disliked being called fat, but sometimes made jokes about his own size.
When Cross was sad about Ben being away, Moss talked to her and also had noticed her pregnancy. He told her to take good care of her pups. The dogs had rumors about Moss liking Cross, but this was never confirmed.
Hyena lied to Moss that Ben was going to attack his pack. Sniper killed one of his subordinates, Lloyd, and tried to kill Jaguar, Moss's son, and blamed it all on Ben's pack. Moss believed this plan and fought against Ben's pack. At one point, Moss pushed huge boulders on Ben's pack.
Moss adopted Chibi (later named Tesshin) in episode 13, and went to Mutsu with Jaguar and the rest of his pack to recruit the big "Four Heavenly Kings of Mutsu." The Mutsu Kings trapped Moss and the rest of the dogs in Mutsu's ravine of death, though with the help of Terry and Ben they were able to fight their way out and get the Four Heavenly Kings to join the Ou army.
He was great help in the battle against Akakabuto and his bears thanks to his raw power. Moss survived the final battle against Akakabuto and stayed in the Ou mountains. He loved to play with the pups of Ben and Cross.
Moss helped Kurotora and defeated Raiga with the help of Mutsu Generals and Hakurou. Moss was very angered because the wolves killed his comrades Bill and Bemu. Later, it's found out that their true enemy is Gaia. Moss stayed in Ou due to his age and thus wasn't part of the battle against the evil wolf lord.
Moss had retired and lived in Gunma prefecture as a pet dog. It's unknown what happened to his pack - possibly he gave the leadership to his son Jaguar.
Moss met Mel when the puppy tried to steal food from him. After finding out that Moss is an old Ou soldier, Mel quickly told him about Gin, Weed and Hōgen. Moss decided to follow Mel at once. After a while, Moss left Mel to find more dogs to help in the final battle.
He returned with several dogs including an old friend, Musashi, and his own son, Jaguar.
Moss was captured together with Gin's pack in a gorge. They were kept hostages by Victor.
As they tried to escape, Moss fought fiercely to let Gin, Akame, Kurotora, Tesshin, George, Ken, Jaguar and the rest of the pack escape. However, when Tābō was trapped, Moss managed to save him. Tesshin was the one to notice that Moss stayed behind and immediately charged back with the pack to save him. They pushed back Bozlev's pack and found Moss on the brink of death.
They desperately tried to keep him alive, but it was too late. Whilst his family and comrades trying to save his life, Moss entered a delusional state, and he ended up in a river, with Riki, John, Terry, Smith, Hyena, Akatora, Bill, Benizakura, Great and the rest of the dead Ou soldiers on one side, and Gin, Tesshin, Akame and the other soldiers on the opposite side. Moss knew it was his time, and decided to go to the afterlife.
He was happily reunited with his old Ou comrades. As he does this, his soul leaves his body, and his comrades knew that he is dead. Tābō then crawled out from underneath Moss, and started to cry when he found out that the old soldier was dead. Tesshin threw himself over Moss's body and wept, as do the rest of the pack and howl to the sky in sorrow.
Moss appeared in episode 18, when he came along with Musashi to help Weed and the Ou's army after he was informed by Jerome. With his arrival, and the idea of GB, Kamakiri and his soldiers retreat. He also assisted in the final battle against Hōgen.
- Because of a translation mistake in anime subtitles, some fans thought that Moss and Ben are half-brothers, even though in truth they are completely different purebred dogs and not related. The original wording called them comrades, but it was mistakenly translated as relatives.