Sojiro, born in September, 1861, was born into a farm family as an illegitimate child, and he was looked down on and frequently was abused by the owners of the farm for his questionable birth. After much physical and mental abuse directed at the young boy, he began to bury his emotions as a way to avoid the pain, and he began wearing an ever present smile everywhere he went. This cheery attitude, though, only deepened his abuse and he was given every hard job, every uncomfortable assignment, and every chore that no one else wanted to do. Despite this, he never wavered, and always kept his smiling mask.
One night, soon after the end of the Boshin War, Sojiro was doing the chores when, in the night, he saw a man wrapped in bandages and carrying a sword attack and kill two police officers who appeared to be chasing after him. The man, then noticing Sojiro, ran up and grabbed him, preparing to kill him. Before he could though, he noticed the child's smiling face, and decided to spare him, as long as he was given supplies and new bandages.
The man, introducing himself as Shishio, grew to like Sojiro after he had been rewrapped in bandages, and gave Sojiro a sword, and told the young man that only the strong may survive. He proceeded to hide his new sword underneath the shed he had Shishio hidden in.
Later that day, Sojiro's "family" then attempted to kill him after he had disappeared for too long (when he was attending to Sojiro's needs), and Sojiro began running, hiding underneath the shed. When one of the men began crawling underneath the shed to get hi, and Sojiro, remembering Shishio's words of strength, took the sword he had hidden under the shed and killed the man. He then crawled out from underneath the shed, and, smiling the entire time, he killed the people who had ruined his childhood. Seeing the massacre, Shishio decided to take the boy under his wing, and Sojiro became Shishio's first student.
Assassination of Okubo
In the eleventh year of the Meiji Era, Sojiro had become Shishio's right hand man, and his top assassin. Due to his speed and strength, Sojiro became commonly used by Shishio in the assassination of many major people in the Meiji Era. One of these men was Okubo Toshimichi, who had earned much fame in the Bakumatsu as a warrior, and had become a high ranking member of the government after the Bakumatsu had ended.
On May 14, 1878, Okubo was riding in a carriage to talk to Kenshin Himura, who he was attempting to get to help him with the capture and execution of Shishio. As the carriage continued on it's path, Sojiro quickly jumped on, without even the driver of the carriage did not notice his presents. He then entered the seating compartment and, before Okubo could call for help, and relayed this message from Shishio:
"It was a good idea to send Hitokiri Battosai to kill me, but it will all be in vain. This country will be mine."
He then smiled, saying that is all, and stabbed him, before making a quick and unseen retreat. Later that night, the carriage was attacked by Shimada Ichiro and the Six Satsuma Samurai, who thought of Okubo as a traitor for his defeat of them in the Satsuma war. The seven samurai then proceeded to kill the carriage driver, but when they opened up the compartment he was in, his dead body fell to the ground. Then, in a panic, they stabbed the cadaver, and made the people believe that they were the ones who had killed Okubo. It should be noted though that it is stated that Shishio knew this attack was going to happen, and had used the attack to his advantage, as opposed to it being only a coincidence.
At the scene of the murder, a crowd gathered that day, and among this crowd was Kenshin Himura, and, quickly coming up behind Kenshin, told him not to interfere in Shishio's plans, or he would end up like Okubo, before disappearing into the crowd.
Journey to Kyoto
Sojiro is next seen observing Aoshi Shinomori, the Okashira, as he attempts to find the whereabouts of Kenshin, who had just recently set off for Kyoto. After learning of this fact from another of Kenshin's rivals, Saito Hajime, Aoshi leaves the Kamiya Dojo. He makes his way to the woods in which he had recently been living, but, returning to the graves of his four friends and fellow Oniwabanshu members, who had givn their lives to save the Okashira, he discovers four of Sojiro's men eating on the graves. Aoshi asks (orders) the men to leave, but they ignore him, instead attacking him for his command, only to be swiftly and mercilessly cut down by Aoshi.
After seeing this display of power from the man, Sojiro jumps down from his perch, revealing himself to the Okashira. Then, after Aoshi asks Sojiro if he works for Shishio, he introduces himself, telling him that almost no one is closer to Shishio then himself. He then asks Aoshi if he will join Shishio as he attempts to take over Kyoto, but Aoshi refuses, saying that he can never serve a man who throws away his men’s life so sparingly. Sojiro then accepts this, but he still asks him if he is willing to miss the changing of an era.