Knuckle used to be a hunting dog living with a human. However, his owner was killed by the bears roaming the forest around his home. Afterwards, Knuckle became a wild dog obsessed with the wish of avenging his owner. He is under the command of Liger.

Knuckle meets Kotetsu and Koyuki in the forest and tells them of the bear threat in the area. He has lost many comrades in the fights against them. As they talk, a bear surprises them. Knuckle follows the bear and gets wounded. With the help of Weed, he is carried back to Weed's brother Joe's owner Ninomiya, for tending their wounds.

As he gets better, he follows Joe to the forest once more to defeat the bears. In the forest, he enters a fight with the enormous bear, the Hybrid Grizzly bear. Knuckle gets crushed under the Hybrid Grizzly bear's paws, as he tries to make an attack.