Name: Hiro
Japanese name: ヒロ
Sex: Male
Breed: Great Pyrenees

When Hiro was a puppy, he and his father, Yukimasa, was attacked by the Irish wolfhound, Kamakiri. Hiro tried to safe his father, but lost his eye in the attempt. His father was killed and Hiro swore to get revenge.

Hiro appears suddenly and without warning in the story. He saves the female Reika, by using his special attack (which is to rip off the testicles of his competent). Reika tells Hiro that Gin, the great leader of Ou, is in trouble and Hiro rushes to help. He fights bravely, but along with Gin and his comrade John, he's taken prisoner by the Great Dane, Hougen. After a while, Hiro, John and Reika manage to escape. As they press forward, they notice they're being followed. Hiro warns John not to stay behind and fight Hougen because of his wounds, but John didn't want to listen. Hiro leaves John to take Reika to safety.

When John is killed by Hougen, Hiro joins Weed and decides to help him find more dogs to defeat Hougen and his soldiers. Finally, Hiro gets his chance to get revenge when the Weed's group faces his father's killer, Kamakiri. Hiro fights him for a long time and when it seemed like Kamakiri would win; Hiro jumps up and rips off his testicals, leaving Kamakiri deadly wounded in the mountains. Hiro has now avenged his father's death.

After the final battle, Hiro falls in love with Reika and together they have four puppies.

In the Hokkaido arc, Hiro volunteers to go with Weed to save Gin's group, who has been caught in a gorge by Victor.