Otsuya no Kata おつやの方
Castellan of Iwamura castle (De facto Toyama clan head)
Incumbent
Assumed office 1572
Preceded by	Tōyama Kagetō
Personal details
Died	December 1575
Spouse(s)	Tōyama Kagetō Akiyama Nobutomo
Relatives	Oda Nobunaga (nephew) Oichi (niece)
Military service
Allegiance	Oda clan Takeda clan
Unit	Toyama clan
Battles/wars	Siege of Iwamura castle

Lady Otsuya (おつやの方 Otsuya no Kata) was a Japanese female samurai (onna-musha) from the Sengoku period. She was the ruler of Iwamura Castle until the last days of her life.

According to legend, Otsuya is best known for the aunt of the famous samurai Oda Nobunaga, the wife of Tōyama Kagetō and foster mother of Oda Katsunaga. She also having conspired against the Oda clan and fought against her nephew, Oda Nobunaga. Her execution under Nobunaga may have been one of the reasons for the decline in Nobunaga's reputation, who would later be murdered by Akechi Mitsuhide and other traitors in the Incident of Honnoji.

Otsuya no kata was the daughter of Oda Nobusada, a warlord in the country of Owari. She was the sister of Oda Nobuhide (Nobunaga's father). She married Tōyama Kagetō, the lord of Iwamura Castle and retainer of the Oda clan. The Iwamura Castle is one of Japan’s three major mountain castles located in Ena City, Gifu.^{[citation needed]}

Iwamura is the highest castle in Japan built atop a 717-meter-high peak by taking advantage of the steepness of the mountain that has a 180-meter altitude difference. The castle has survived 700 years. It is also known as the “Misty Castle” because even the climate worked in favor of the castle by hiding it from enemies with a blanket of fog.^{[citation needed]}

The Iwamura Castle was a battlefield from 1572 to 1575. At the apex of the anti-Nobunaga coalition, in 1572, Takeda Shingen ordered Akiyama Nobutomo, one of the "Twenty-Four Generals" of Shingen, to attack the castle, but Otsuya and her husband were prepared to defend. After days of resistance, Tōyama Kagetō, the commander of the castle's garrison, fell ill and died. Lady Otsuya became the female lord of Iwamura castle. Toyama used to be subordinate to Takeda, but at that time Lady Otsuya had a hostile relationship with Takeda. She didn't surrender for months and continued to defend the castle until March 6, 1572, when she made an agreement with the Takeda clan. Akiyama Nobutomo negotiated the castle's surrender with Lady Otsuya, and she settled in a peace treaty without bloodshed and ceased attacks. The adopted son of Otsuya and the official keeper of the castle, a seven-year-old lord called Gobōmaru (Oda Katsunaga) was taken to the Takeda home in the province of Kai as a hostage. In accordance with the surrender treaty, Lady Otsuya married Akiyama. Otsuya surrendered the castle to the Takeda and became a member of it and an enemy of Nobunaga. This caused the Takeda-Oda relationship to decline and Nobunaga started a campaign against the Takeda clan.

On January 25, 1573, the Battle of Mikatagahara took place, On March 15, 800-soldiers led by Baba Nobuharu, who were attacking Iwamura Castle, attacked the Oda Army and Oda Nobunaga pulled 10,000 soldiers. When Nobunaga learned that the soldiers at Iwamura's castle, led by his aunt, had attacked the troops of the Oda clan, he decided to counterattack.^[1] On April 12, 1573, Takeda Shingen died, and on December 22 of the same year, an event that led Lady Otsuya to lead the defense of Iwamura Castle once again.^{[citation needed]}

In 1575 when Oda army defeated the army of Shingen's son, Takeda Katsuyori, in the Battle of Nagashino, Oda Nobutada and others surrounded Iwamura castle. Oda Nobunaga decided to attack and take his aunt's castle, but she defended it against Oda's fierce assault for a half a year. After six months of battle, she left the castle to respond to Oda's false plea for peace. However, Nobunaga reneged on his word and had Otsuya and Nobutomo crucified as traitors on December 23, 1575.^[2]

Representative from Ena City Board of Educational and Cultural Affairs Division has stated that Lady Otsuya has become a basis of popular legend as "female daimyo" who possessing "unmatched beauty." and was also "aunt of Nobunaga" in many novels and anecdotes of the era following Sengoku period. This legend was inspiring many literature works or fictional novels. However, this legend of a female castle lord has no historical sources and no basis, as it only appeared through anecdotes from the later era such as Kōyō Gunkan or ``Iwamura Fushi.^[3]

Since 1992, the residents living close to Iwamura, Ena City, Gifu Prefecture, have hung a short [split] curtain hung at the entrance of a room indicating the names of female members of each family to the memory of Otsuya no kata, who was the castellan of the area.^{[citation needed]}

• List of female castellans in Japan