Hidetsuna Kozumi was a samurai in Japan's Sengoku period famous for creating the Shinkage-ryu school of combat.
Background
Hidetsuna Kozumi was born as Kamiizumi Hidetsuna in his family castle in Kōzuke Province (modern day Maebashi, Gunma Prefecture). His family were minor landed lords in the service of the Yamanouchi branch of the Uesugi clan. At the time of his birth, Kōzuke Province was being contested by the Uesugi, the Hojo, and the Takeda clans. His family was originally a branch of the Ogo clan that moved to nearby Kaigayago Kamiizumi and took its name for their own. When the main Ogo clan moved to Musashi Province, the Kamiizumi family took over Ogo Castle, at the southern foot of Mount Akagi.
Education
From the age of 13 or 14, Kamiizumi was tutored by a Zen rōshi named Tenmyo in Zen Buddhism and other Eastern philosophy. In his youth, he went to nearby Shimōsa Province (modern day Chiba Prefecture) and began studying Nen-ryu, and Shintō-ryū. Later he went to Hitachi Province (modern day Ibaraki Prefecture) and studied Kage-ryu.
Career
In 1555, Hojo Ujiyasu ordered an attack on Ogo castle, now commanded by Kamiizumi. Kamiizumi surrendered the castle without a fight, and joined Ujiyasu. This same year, Uesugi Kenshin invaded western Kozuke in order to re-take Hirai Castle. Kamiizumi abandoned the Hojo side, and sent messages to the Uesugi. He became one of Uesugi's generals, and helped the Uesugi drive out the Hojo forces. Kenshin seized total control of Kozuke, installed Nagano Narimasa as governor in Minowa Castle, and returned to his base in Echigo.
Kamiizumi joined Nagano's service, and quickly became one of the "Sixteen Spears of Nagano House". In particular he distinguished himself when Nagano attacked Yamanaka Castle, and became known as "the best spearsman of Kozuke". Nagano held off attacks from Takeda Shingen for seven years from Minowa Castle, but he died in 1561. His heir, Ukyō-no-shin Narimori, was only 16 years old, so Nagano’s death was kept secret as long as possible. Shingen eventually found out, and in 1563 (some sources suggest 1566), he invaded western Kozuke with a force of over 10,000 Kai soldiers. The Koyo Gunkan dates the invasion to 1563, while the records of Chōnenji, the temple where Nagano was buried, dates it to 1566. Minowa Castle was completely surrounded and besieged. Narimori took his own life on February 22, morale fell, and the castle followed on the 28th.
Kamiizumi fought his way out of the castle, and escaped to eastern Kozuke, where he joined with Kiryu Oinosuke Naotsuna. But Naotsuna died soon thereafter and his son Matajiro Shigetsuna took over. With this, Kamiizumi returned to Minowa Castle.
