Utsuzuo born into the Mashiroi Group as the only son and heir of the group's leader, Mashiroi Kaguzou. When he was a child, his father introduced him to Nakamura Kyoujirou, a boy of his age, who was recently accepted into the group and became his bodyguard and friend.
Once while out walking, Utsuzou was attacked by a enemy group and Kyoujirou used his body to protect him, ended up with a big cut across his left eye as a result. Upon returning home, a crying Utsuzuo rushed into his father's arms only to see him rushing over to hug the injured Kyoujirou in relief that he was all right. Because of this, Utsuzuo developed an inferiority complex towards Kyoujirou, whom his father also viewed as his own son. However, the two boys remained as close friends, even to the point of being blood brothers.
Kyoujirou claimed to have killed Utsuzou in order to make way for his own ascension to power within the group, when in actual fact that he had killed himself by hanging five years before the Gintama storyline took place. Presumably, Kyoujirou lied to protect his father from heartbreak and guilt since it was his drastic actions to force Utsuzou into becoming heir to the group that led to him holing himself up inside the store house, where he eventually hung himself.
Utsuzou loved his father but he did not want to follow his footsteps of becoming a yakuza. Instead, he wanted to be a kimono designer. His father's actions eventually led to his suicide.
Kyoujirou was the only person Utsuzuo really trusted. The two were close friends since childhood and even viewed each other as brothers. Kyoujirou lied about his death to protect their father from heartbreak and guilt.