Ryu is Tetsuzou Nihei's bear-dog.
Ryu is an Ainu-ken, which is also called Hokkaido Dog. He has a typical spitz-dog appearance, such as small pricked ears, a curled tail resting on his back, and relatively short legs. He has urajiro colouring, and darker fur on his back.
Ryu is a very intelligent dog, companion and loyal (tried to defend Nihei from wolves and helped in the fight against Sugimoto).
According to Nihei, Ryu was trained by the Ainus to be fearless when placed against a bear. I'll even send him forward to a bear's burrow coming out for the attack. Ryu follows Nihei and Tanigaki leading towards the territory of the Retar, where it showed the removal in entering the region, being dragged by the collar. He then follows them to where Sugimoto, Asirpa and Retar killed the deer.
Then his group lay close to the flesh, waiting for the wolf, although Ryu was a little scared. In the second attempt of cornering the animal, Nihei came across Sugimoto and his group. Ryu advanced towards the soldier, preventing him from using the rifle, giving the chance of its owner to attack. In the midst of confusion he had a brief confrontation with Shiraishi, making it impossible for him to take the gun, even though it was thrown downhill.
Ryu tried to protect Nihei from Retar and his family, though their owner gave up by leaning against him, the dog crying in his lap. He was then taken to Asirpa village along with Tanigaki.
(From chapter 70 onward)
When Tanigaki played with a shell toy that Osoma gave him and injured himself in the process, Ryu can be seen watching silently as Osoma hurries to get Huci to treat Tanigaki.
Ryu follows Cikapasi and Enonoka as they successfully rescue Enonoka's dog from the chatty Russian. Later, he runs alongside Enonoka's dog as the four of them head back to rejoin the rest of their group.
Ryu is equipped as a sled-pulling dog alongside several of Enonoka's dogs as Sugimoto's group heads to the national border north from Toyohara through heavy blizzard. As they travelled, Ryu attempts to break away from the line but Sugimoto yells at him to stay in formation. Tanigaki wonders if there is a reason Ryu did that but Sugimoto dismisses him saying that Ryu is not suited for pulling sleds as he is just a hunting dog. However, unbeknownst to them, Ryu was the only dog that managed to follow Enonoka's sled.
Now lost, Sugimoto and Tanigaki attempts to dig a hole in the midst of the snowstorm, while Ryu and Cikapasi both are affected by the sheer cold surrounding them. Once they had a small makeshift shelter built up, Tanigaki gets Ryu and the sled dogs to huddle around them so that they can stay warm. Sugimoto, Tanigaki, and Cikapasi were able to find warmth in a nearby building thanks to a lighthouse that Tsukishima and Koito had activated. Once they had gotten warm enough, they helped Enonoka's grandfather build a new sled, and Tanigaki notes that during the snowstorm, Ryu had tried to leave the line in order to follow the other sled. Sugimoto then begins to pet Ryu, apologizing for doubting him. Sometime later, as Sugimoto's group left the lighthouse, Ryu is left in charge of pulling the sled once more.
Eventually, when Sugimoto's Group got closer to Akou Prison, they hear a loud explosion and sees smoke flowing in the distance. Using his binoculars, Tsukishima tells everyone that the smoke is coming from Akou Prison. Upon arriving at Akou Prison, they find that they were too late as Asirpa's Group has already left, so Sugimoto has Ryu sniff out Asirpa's scent. Suddenly, an Amur tiger comes out from the hole in the walls of the prison, causing Ryu and the dogs to run as Tanigaki and Tsukishima shoots at the tiger, scaring it away.
Sugimoto's Group attempts to look for Asirpa's Group but their sleds are unable to maneuver across the drift ice as it has become too rough and uneven and Tanigaki warns that the weather might get worse, saying that it would be too dangerous to go after Asirpa's Group. However, Sugimoto is adamant that Asirpa is close and cuts Ryu's leash to go look for her. They eventually find Shiraishi and the three of them prepares to look for Asirpa next. As they run around the frozen plains, the ice below them suddenly begins to break and they get stuck on a small block of ice that begins to drift away from the other ice platforms.
However, by utilizing the hoparata technique that Sugimoto learned from Asirpa, they are able to get back onto the mainland. The three of them are able to find Asirpa and as Sugimoto reunites with her, Ryu tries to join them but Shiraishi holds his leash back so as to not get in the way of their emotional reunion.