Anyoin Temple, the former temple of Sainenji, was established by Hattori Hanzo Masanari in 1593 at Edo Kojimachi. Hattori Hanzo was the head of Tokugawa Iga Ninja and Koga Ninja. He served his lord Tokugawa Ieyasu for all his life, and because of his great sucess, he was also one of Tokugawa 16 great Generals. He was the master of spear, and known as "Hanzo, the Ogre."
In 1579, Nobuyasu was ordered to do Seppuku by Oda Nobunaga, his father in law because he was putted under suspicion to betray Nobunaga and ran for Takeda clan. There was no proof that Nobuyasu betrayed Nobunaga, but Nobunaga believed the information and didn't change his mind.
Hanzo was chosen for Nobuyasu's Kaisyaku. Kaisyaku is the person who cut the head of Seppuku person off to finish. However, he cried and rejected to do Kaisyaku. He said "I've been serving 3 generation of lords of Tokugawa, and there is no way to arm my sword to my own lord."
When Ieyasu hard that, he valued Hanzo's loyalty to Tokugawa when he heard that, and said "He was entitled as the Ogre, but still couldn't kill his own lord."
When Ieyasu moved to Edo, Hanzo moved to Edo Kojimachi which is located west side of Edo Castle. He made a grave of Nobuyas and buried the hair of Nobuyasu which he called all the time. Then he became the buddhist priest, and named himself "Sainen." Ieyasu donated a gold to built Nobuyasu's memorial temple to Hanzo, but before he finished build a temple, he died in December 23, 1596.
The name of Sainenji is named after Hanzo's buddhist name.
He was buried also at Anyoin Temple.
In 1634, Sainenji was moved from Kojimachi to current location. The temple was lost during WWII, and reconstructed in 1961.
Spear of Hattori Hanzo
258cm length remains and 7.5kg. It was originally 4.2m length. This spear was given by Tokugawa Ieyasu for the prize of the battle of Mikatagahara.