Thunder is a well-known assassin and, with his older brother Lecter, forms a feared assassin duo called Killer Fang. He is Murder S's minion and one of his best apprentices in the manga and one of Hougen & Genba's top hitmen in the anime.
Thunder is a black and tan furred Doberman with tall floppy ears and brown marks on his face. His teeth are implied to be either made of steel or coated with it.
He is sadistic along with his brother and enjoy torturing his victims before killing them.
Ginga Densetsu Weed
Thunder was trained by Sniper, known as Murder S, and was his best apprentice along with his brother. He has extremely sharp fangs, strongly hinted to be steel-coated.
After his master allied with Hōgen, he and his brother were sent to murder Kyōshirō. They meet Teru's father and force him to help them. When they're about to attack Kyōshirō, Weed shows up and thus they leave the scene. However, Kyōshirō heard them and sent Hachi and Rick after them. Thunder and Lecter easily ambush the two followers, but they run away when GB and Rocket show up.
Quickly after this, they manage to kidnap Teru and plan to use him as a hostage. However, they soon let go of the puppy when they hear Weed's identity. Thunder fights Weed while his brother fights Kyōshirō. Thunder is at first annoyed by the fast opponent who only avoids attacks, but slowly Weed's bear hound blood starts to flow and he starts to fight back.
Weed rips off the tip of Thunder's nose and then breaks his fangs with a branch. Wounded Thunder collapses on the ground and is unable to fight for a while. He scolds at Teru's father who runs away from the battle. Later in the fight, Thunder manages to make a surprise attack and catches Weed. He stops Weed from helping Teru, Teru's father and Kyōshirō.
When the Ōu army shows up, GB and Sasuke attack and chase Thunder who quickly lets go of Weed. Hiro throws wounded Lecter on his back. Thunder starts to shake and cry as he thinks his brother is dead. Weed tells him to leave and he does, but is soon followed by his brother who isn't dead after all. The two assassin brothers disappear and are not seen again in the series.
In the anime, Thunder was a member of Hōgen's pack and was trained by humans.
He used to be as the same military facilities as Jerome but he and his brother were transferred to get specialized in their fangs. They appeared in episode 10 where they make Teru's father help them at finding Weed and Kyōshirō.
As the fight breaks lose, Thunder fights Weed, but as Weed's pack appears he and his brother try to flee, but gets spared by Weed in the end.Thunder and his brother returns again to try and finish the job on killing Weed and ends up in a fight with Weed and Tesshin which they lose.Yet again their lives is spared by Weed, but is told to not work for Hōgen again.
As they flee they start planning on how to kill Weed which Jerome hears and then decides they're too dangerous to be kept alive and then kills them. Weed and the others came to where Jerome was about to kill Thunder after hearing Lecter's dying scream, where after finding Lecter's body did they heard Thunder shouting for help. Thunder who was pinned by Jerome, begs for his life and promised to not go after Weed anymore. Jerome just said: "There's no point in arguing".
Thunder begs again only for Jerome to grab Thunder's neck with his jaws. Weed who had just arrive asked Jerome what's he's doing then order him to let Thunder go. However Jerome told Weed that Lecter and Thunder were planning on going after him again, and that killing them is the only option. Weed replied that he didn't care, and orders Jerome to let Thunder go, for he won't forgive any self-fish actions.
As Weed runs and tries to stop him, Jerome crushes Thunder's neck and died with one last scream right in front of everyone. Although Jerome was able to save Weed from a future attack from Thunder and Lecter, his actions caused Weed to hate him and banished him from his pack for taking lives. Thunder was the second of the brothers to die.