Kōsaka Jinnai was a notorious swordsman, mercenary, and thief who commanded a gang of thieves in 17th-century Edo (modern Tokyo). According to legends, it's believed he was originally a samurai or ninja belonging to the Takeda Shingen clan. It's also believed he was once the apprentice of famed swordsman Musashi Miyamoto, however, this may have been a widespread rumor because of his marvelous swordsmanship. 

After the Tokugawa clan won the Battle of Sekigahara in 1600 and established a new bakufu (shogunate) based in Edo, Jinnai became a mercenary, hunting down the remnants of rival clans. He helped make numerous arrests, including taking down the infamous ninja-turned-thief, Kotaro Fuma, who had been his personal nemesis.

Jinnai continued his mercenary work across the Kanto region, that was until the shogunate began to feel threatened by his growing influence and deeds. The hunter soon became the hunted. In 1613, nearly a decade after the shogunate’s betrayal, Jinnai was captured by the authorities for breaching public order.

Before he was crucified for his crimes, Jinnai stated that if it weren’t for his ague (malaria) he wouldn’t have been caught. He also exclaimed that his spirit would remain here long after his death and heal those who contracted malaria and prayed to him. 

Sometime later, a shrine was constructed near the bridge leading to his execution site. Many people flocked to the shrine to pray for good health. It was eventually lost to a fire during the Great Kanto Earthquake of 1923. In 1930, it was reconstructed at a different location. During the anniversary of Jinnai’s death on August 12, you can still find dozens of people at the shrine paying their respects and hoping for good health.