The founder of Tenshinsho Jigen-ryu, Kaiso Setoguchi Bizen no Kami Masamoto was born in 1431 during the 3rd year of Eikyo in Satake, Hitachi Ibaraki prefecture into the Kose (Tose) family under the name Nagamune.  

From an early age Nagamune showed a special interest and ability for the sword and started learning from the Hitachi Kashima Shinto priests. At the age of 16 he formally started training in Tenshin Shoden Katori Shinto-ryu; and at 22 he received Menkyo Kaiden (Certificate of mastership). He also learned and received certificates from Yaobettoh Kenko, founder of Jiken-ryu.  

According to the hand written records of the school in 1460 while meditating at Kashima shrine he received a revelation and became enlightened. At this time he called these techniques he had created "Tenshinsho Jiken-ryu".  

In 1467 he joined the Yamana Sozen side and participates in the “Onin war” and after four years he decided to go on a journey across Japan before finally settling in Satsuma in 1482. and becoming a vassal of the Shimazu Clan. Once in Satsuma his impressive sword skills made him an important figure among the Satsuma clan and he was adopted into the Setoguchi family, changing his name to Setoguchi Masamoto. His son and heir Gennoshin, who later on in life would become the 2nd Soke of Tenshinsho Jigen-ryu, was born in 1486 during the 18th year of Bunmei. Masamoto was 55 years old at the time.  

Setoguchi Masamoto left a few writings containing the secrets of his school. In 1497 he completed the writings of “Tenshinsho Jiken-ryu Hidensho”, a series of three manuscripts (Sonkei, Sakken and Chousho) and  “Tengenroku” in 1512.  

In 1508 he decided to change the name Jiken-ryu to Jigen-ryu. Following the lineage to Jigensai and Minamoto, Setoguchi 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” means all those different styles and also refers to Jigensai’s “Gen”, 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 “Hyohou” of the Minamoto clan, and the source of mind. I hereby name my style as Tenshinsho Jigen-ryu Hyohou with absolute certainty and confidence”.  

Kaiso Setoguchi Bizen no Kami Masamoto, the founder of Tenshinsho Jigen-ryu Hyohou passed away on September 23rd, 1518 at the age of 87, during the fifteen-year of Eisho when the Sengoku Jidai or Warring states period was beginning, but left behind a legacy that would influence and shape the spirit of the Satsuma warriors forever.

From right to left: Jigen ryu Sakken no Maki, Jigen ryu Chousho no Maki, Jigen ryu Sonkei no Maki, Sankan no Hiden, Sanso Hiden, Ryuko no Maki.