Musashi, originally called Kowaka, is the son of the great female fighting dog Seiran.
His best friend is Yamato, and he's like a brother to him.
He is brown Tosa with brown eyes and wear blue collar.
Unlike his mother he is extremely cowardly which is shown throughout the course of the series.
Shiroi Senshi Yamato
He falls into a truck and wanders alone until Yamato find and save him from the clutches of an eagle. Yamato takes puppy to his owner, Ryo Fujiwara. The family decides to keep the puppy and named Musashi after Yamato battleship. Musashi and Yamato will become very close, like brothers. In particular, Ryo's father is appreciated by Musashi hard.
Musashi's family searching for him back home, but his mother and siblings treat it badly. Musashi decides to run away and goes a long way back to the Fujiwara family.
After his mother is beaten badly in her fight against Sahara he and Shiro attempt to beat Sahara themselves avenging Seiran. Right before Seiran dies she manages to rile Musashi with one final roar of encouragement which causes him to lose his fear and help Shiro defeat Sahara.
Hakugin no Teiō>
When the dog thieves abducting Kenichi's father , Ryo call the police and then leaves Yamato, Kenichi and Hayate with thieves in search of a place to hide. Ryo tells Musashi to wait at home until the police force, and then lead them Ryo and other formations. Musashi obeys and leads the police thugs mountain cottage, so that they can be arrested. The next day, the police chief rewards Musashi, Yamato and Hayate "Silver Emperor," the honorary title. Ryo decides to buy the premium money Musashi felt, as a puppy.
See more pictures in Musashi (Puppy)/Gallery