He's a Tosa with brown fur and black markings around his eyes.
He's a ruthless and strong fighter.
Byakuren no Fang
Unryū is first seen when his owner Shinnosuke Anzai takes him to Makoto's home to challenge the Yoshimura family's tosa. Zero (then the "tosa" puppy Chibi) rushes Unryū and is consequently the fighting dog breaks his leg. The Yoshimura family's tosa is critically injured trying to defend Zero, and Unryū walks away victorious. Makoto's father retaliates by bringing Zero to the Anzai home and allowing him to pay Unryū back with a bite to the leg.
When Zero's mother, Silver Fang, comes to take Zero back to Siberia with her, they are stopped by Unryū. Unryū kills Silver Fang and Zero swears to avenge her death.
Eventually, the one year old Zero meets Unryū in a fighting tournament, and Zero beats Unryū to win the first round. Unryū is momentarily replaced by another dog, Beni Gumo, but when Beni Gumo is also defeated Unryū is given a second chance to face Zero in the final match of the tournament.
Both having trained specifically for this final showdown, Unryū nearly defeats and kills Zero, but spurred by his desire to avenge his mother's death, Zero makes a comeback and soundly defeats Unryū to become the new tournament champion.