Soshinni (1588 - April 5, 1675) was a daughter of Toshisada MAKIMURA who was a lord of the Iwate castle in the Ise province and nun served Iemitsu TOKUGAWA, the third seii taishogun (great general) of the Edo bakufu (Japanese feudal government headed by a shogun) in the Edo Period. She was also called Ona-a, Onou, or Kona. She was a niece-in-law of Kasuga no tsubone, who dominated O-oku (inner halls of Edo Castle where the wife of the Shogun and her servants reside) in the same period, and served as an assistant asked by Kasuga no tsubone. She was Kaiki (patron of a temple in its founding) of the Saisho-ji Temple in the Rinzai sect. She first married with Naotomo MAEDA, but was forced to divorce, and married again with Yukikazu MACHINO. Ushinosuke MAKIMURA was her younger brother.
Ona-a (later Soshinni) was born as a daughter of Toshisada MAKIMURA who was a lord of the Iwate castle in the Ise province in 1588. However, her father joined the Bunroku-Keicho War caused by Hideyoshi TOYOTOMI who he was serving and died in 1593. Ona-a was taken care of by the Maeda family in the Kaga domain guided by Toshiie MAEDA who had been close to her father and raised with Toshitsune MAEDA. Ona-a was grown up in due course and married with Naotomo Maeda in the Komatsu-jo Castle (the son of Ko, the first daughter of Toshiie), a branch family of the Maeda family, and had two sons, but she was suddenly forced to divorce from the Maeda family. The reason of this divorce was unknown with various theories and one of them was that she was close to Ukon TAKAYAMA, a Christian daimyo (Christian feudal lord).
After the divorce, Ona-a took her youngest son and stayed with Icchu-zenji (master of Zen Buddhism), who was her younger uncle and a chief priest in 'Zakke-in Temple' of the Myoshin-ji Temple in Kyoto established by her father while in life. Soon she remarried with Yukikazu MACHINO who was a senior vassal of Tadasato GAMO, the lord of the Aizu domain, and exerted power as a wife of the senior vassal, but their lord Tadasato GAMO died not so long afterward and the rank of the Gamo Family was forfeited because there was no successor and her husband became ronin (masterless samurai).
Being a ronin family, they moved to Edo and Ona-a read many books because she had plenty of spare time and acquired a wide range of knowledge and education. After that, Kasuga no tsubone who was Ona-a's aunt and dominated O-oku of that time highly regarded Ona-a's education and asked her to serve as own assistant, and so she started to work at O-oku.
Ona-a entered O-oku and made efforts to improve awareness of maids by utilizing experiences acquired in the Zakke-in Temple, such as expostulating Zen mind to women in O-oku. Moreover, she called Jishoin, her own granddaughter, in O-oku asked by Kasuga no tsubone as an adopted daughter of Kasuga no Tsubone and made her a concubine of Iemitsu (called Ofuri-no-kata). In 1637, Ofuri-no-kata had Chiyohime, the first daughter of Iemitsu (later became the wife of Mitsutomo TOKUGAWA, the lord of the Owari domain), but her health deteriorated due to the childbirth and Ona-a nursed her (Ofuri-no-kata died in 1640 in spite of Ona-a's nursing).
While spending such days, Ona-a became a priestess and announced her name as 'Soshinni' in 1643 with a recommendation of Iemitsu as one of the reasons.
Soshinni preached Zen even to Iemitsu, and soon after that he donated the land which was the site of residence of Ryukei OHASHI, a former private secretary of the bakufu, to Soshinni and instructed to erect a temple, and thereby the Saisho-ji Temple was erected with Soshinni as its kaiki. Iemitsu called in Soshinni at his deathbed and left words that "This body shall be buried in Nikko, but my sole shall stay in this Saisho-ji Temple".
After the death of Iemitsu, Soshinni left O-oku and spent the rest of her life in the Saisho-ji Temple.