Harada Sanosuke (原田 左之助 1840 - July 6, 1868) was a Japanese samurai who lived in the late Edo period. He served as captain of the 10th Shinsengumi unit and died during the Boshin War.
Harada was born into a family of chūgen, a group of low-ranking warriors, who served as servants of the I-yo Matsuyama domain (now Matsuyama City (Ehime).
Harada was trained in the use of the spear under the Hozoin-ryu technique, so he usually preferred the use of the spear rather than the sword on the battlefield.
During his stay at Matsuyama, he was once ridiculed by one of Matsuyama's servants who claimed that as he was only a peon, he would not be familiar with the application of seppuku so he immediately drew his sword and attempted it, however the wound was superficial and he survived.
After leaving Matsuyama's domain, he went to Edo and trained at Kondō Isami's dojo.
In 1863, Harada along with Kondō and a few others joined Kiyokawa Hachirō's Roushigumi, but soon after Kondō and Serizawa Kamo broke away and formed the nucleus of what would later become known as the Shinsengumi.
Harada became the captain of the tenth Shinsengumi unit. He trained briefly at a dojo run by Tani Sanjūrō, whom he introduced to the Shinsengumi. In 1865, Tani became the captain of the seventh unit. In Kyoto, Harada married a woman named Masa, with whom he had a son named Shigeru (茂).
Harada enjoyed the confidence of Vice-Admiral Hujitaka and was involved in many crucial missions including the assassination of Serizawa Kamo, who had originally been the commander of the Shinsengumi.
Among the missions he was also involved in were the assassination of Uchiyama Hikojirō, the "Ikedaya Incident" and the elimination of the Kōdaiji faction of Itō Kashitarō. Harada became hatamoto with the rest of the Shinsengumi in 1867.
Harada was accused of murdering the famous Sakamoto Ryōma and although the nature of the murder was never clarified, according to the confession of a Tokugawa servant named Imai Nobuo, Ryōma's killers were men of the Mimawarigumi (another Tokugawa-affiliated unit) under the orders of the hatamoto Sasaki Tadasaburō.
Harada along with the rest of the Shinsengumi fought at the Battle of Toba-Fushimi and subsequently along with his family left Kyoto to move to Edo.
He joined the Shinsengumi vanguard to Kai Province and fought at the Battle of Kōshū-Katsunuma, where they were forced to retreat and withdraw. After this defeat both Harada and Nagakura left the Shinsengumi after a series of disagreements with Kondō and Hijikata.
According to Nakamura's version, Kondō sought to have the survivors become his servants so Harada, Nagakura and some others adamantly refused, joining another group of Tokugawa servants forming a new unit, the Seiheitai.
The Seiheitai left Edo shortly after the fall of Edo Castle and headed north, seeking to join the fighting near Aizu.
He is believed to have died at the age of 28. After the Seiheitai left Edo, Harada, who sought to see his wife and son, returned to the city. Because it was impossible for him to leave the city he joined the Shōgitai, which were also on the side of the Tokugawa regime.
Harada fought in the Battle of Ueno, where he was mortally wounded by gunfire. He died two days later from wounds at the residence of the hatamoto Jinbo Yamashiro-no-kami.
After his death a rumor spread that Harada did not die in 1868 but survived and traveled to China, where he became the leader of a group of bandits on horseback.
There were reports that an old Japanese man came to the aid of the Imperial Japanese Navy in the First Sino-Japanese War who claimed to be Harada Sanosuke. This was reported in the newspapers in 1965 but could never be confirmed.