Name: Kotetsu
Japanese name: 小鉄
Sex: Male
Breed: Kishu

Kotetsu is Koyuki's younger brother. He is very young and quite a small rebellion. He runs away from home andKoyuki tries to find him. She gets caught in a trap, but Weed saves her. She asks him to help her find her brother, and Weed does.

Meanwhile Kotetsu is attacked by the stray Yuusuke and his gang. Kotetsu however loses his tail during the fight. He is rescued by Weed. When Koyuki is taken away by their master to become a breeding dog, Kotetsu runs to Weed to tell him what has happened.

As Weed and Koyuki falls in love, they start a small journey together to be alone and care for their growing relationship. However, Kotetsu miss his sister so much that he starts a journey to find her. When Kotetsu finds her, Weed leaves the care of Koyuki to him, as he has to go and aid his father in the battle against the Russian invader, Victor in Hokkaido.

In the Hybrid bear arc, Kotetsu meets the red puppy Koujiro as he hunts a small rabbit for his sister. Koujiro has killed Kotetsu's prey. As they discuss who the kill belongs to, they are ambushed by the Hybrid Grizzly bear. However, Koujiro's father is nearby and he, along with his pack mates, scares the bear off. Shortly after, he and his sister reunited with Weed, who has come to search for them.

When the battle against the Hybrid bear begins, Kotetsu is taken to safety in a cave along with Koyuki and Koujiro. He survives the battle and reunites with Weed's pack.