The origin of Tenshinsho Jigen Ryu is Jouko ryu Kashima no Tachi Hakugen ryu (上古流鹿島之太刀白源流) founded in 931 A.D. by Jigensai Kazutou Jiichibou (自源齋一任自一坊) during the 2nd year of Jouhei. Hakugen ryu was based on Kashima no Tachi Shinmyoken (鹿島之太刀神妙剣) which was founded by Kunima Masato (國摩真人) in early 400 A.D. and it is regarded as the first sword school of Japan.

Jigensai created a technique called Tenshinken (天眞剣) and set it as the secret of Hakugen ryu. Hakugen ryu was then inherited by the Minamoto clan and eventually became Minamoto ryu. There were two unique forms in Minamoto ryu; one was called Ten Chi Jin Sandan no Houkei (天地人三段之法形, the form of the three techniques of Heaven, Earth and Human). Its secret was embedded into a set of two scrolls, "Ryuko Nikan no Hidensho" (龍虎ニ巻之秘伝書, the two secret scrolls of Dragon and Tiger) and inherited by Minamoto no Yoshie (源義家 1039 - 1106).

Yoshie decoded the secrets and created a system which he called "Ten Chi Jin In Yo Godan no Houkei" (天地人陰陽五段之法形, the form of five techniques of Heaven, Earth, Human, Darkness and Light). This was the other basic principle in Mianamoto Ryu.

The scrolls and the secrets were then inherited by Kiichi Hougan (鬼一法眼) and he taught them to Mianamoto no Yoshitsune (源 義経, 1159 - 1189), who founded Mianamoto ryu based on them. It was then passed down to the Oide clan, the Urabe clan (priests of Kashima) and to Yaobettoh Kenko (founder of Jiken ryu)  by Shunjobu Jugen (俊乗坊重源).Yaobettoh wrote a scroll named Jiken ryu Ryuko no Kan (自顕流龍虎之巻, the Jiken ryu scroll of Dragon and Tiger). 

By this time Oze Yozaemon'i Nagamune (小瀬与左衛門尉長宗), a samurai from Joshu Kasama (常州笠間, the old name for Ibaraki prefecture today) who had received a Menkyo Kaiden in Tenshin Shoden Katori Shinto ryu (天眞正伝香取神道流) from its third inheritor Iishino Morichika, had heard of Yaobettoh's Jiken ryu and decided to challenge the school to three matches, Oze lost all three of them so decided to study Jiken ryu under Yaobettoh.

After some years of practice he inherited the two forms of Minamoto ryu, "Ten Chi Jin Sandan no Houkei", "Ten Chi Jin In Yo Godan no Houkei" and the Jiken ryu scroll "Jiken ryu Ryuko no Kan" and left to test his skills as a warrior.

According to the legend he stopped at Kashima Jingu where he stayed meditating for three years. When he came out and after receiving divine inspiration form the Kami of the shrine, it is said that he was able to cut down a flying swallow in mid air. He then  decided to follow the connection with the Minamoto clan and requested lands in Satsuma (薩摩) (present day Kagoshima) bringing along with him a unique sword style that he called Tenshinsho Jiken ryu (天眞正自顕流).

"Tenshinsho" (天眞正) represents Kashima Katori Myojin (鹿島香取明神), "Ji" () was taken from the original founder's name Jiichibou, and "Ken" () was taken from his previous master Yaobettoh Kenko. There in Satsuma, Nagamune gained the favor of the Setoguchi, a family of the Hachimangu Shrine in Osumi province, and  so he took the name Kaiso Setoguchi Bizen no Kami Masamoto (瀬戸口備前守政基). This is the beginning of  the Tenshinsho Jigen ryu Hyouhou of Setoguchi Bezen no Kami Masamoto.

In one document about the Tenshinsho Jigen ryu, Nagamune is described as follows: "His birth name was Gentaro, he loved the sword since childhood like nothing else and was strong as a demon. He was a descendant of Minamoto Yoshimitsu". 

Setoguchi Bizen no Kami Masamoto wrote three scrolls that contained the  secrets of his style "Songyou" (尊行), "Sakken" (察見), and "Kikigaki" (聴書). He also wrote "Tenshinsho Jigen ryu Kihon Kyoten/Ugenroku" (天眞正自源流兵法基本教典 / 无源録, the basic and ultimate book in Tenshinsho Jigen ryu Hyouhou) in 1512. 

His sword style was taught to the elite samurai of the Shimazu clan and served as the base for other sword styles that sprung out of Satsuma such as Togo Chui's Jigen ryu (示現流). After many years of training in Satsuma; following the lineage to Jigensai and Minamoto he decided to call his style "Tenshinsho Jigen ryu Hyouhou" (天眞正自源流兵法). He left a note explaining the reason why he changed the name of his style.

"The origin of my style traces back its roots to Jouko ryu Kashima no Tachi Hakugen ryu. The style has incorporated many other different styles by the past successors. "Gen" (源) means all those different styles and also refers to Jigensai's "Gen" (自源齋), the founder of Jouko ryu Kashima no Tachi Hakugen ryu. "Gen" () also contains several meanings like; the source of  everything in the world, the war strategy (Hyouhou, 兵法) of the Minamoto clan, and the source of mind. I hereby name my style as Tenshinsho Jigen ryu Hyouhou (天眞正自源流兵法) with absolute certainty and confidence".

Kaiso Setoguchi Bizen no Kami Masamoto died on 09. 23. 1518, the fifteenth year  of Eisho, when the Sengoku Jidai or warring states period was beginning,  but left hidden in Satsuma the secrets of his style which has been passed down until today. Now Tenshinsho Jigen ryu Hyouhou is headed By Ueno Kagenori Genki (上野景範源己) 28th inheritor and present headmaster, and Ueno Takashi Doushin (上野貴史童心) 29th Soke.