The party left the treaty port of Yokohama at 2:30 in the afternoon by boat, crossing the harbor to Kanagawa village where their horses waited. Richardson rode with Woodthorpe Charles Clark and William Marshall, both Yokohama-based merchants, and Marshall's sister-in-law Margaret Watson Borradaile. They were heading north along the ancient Tokaido road toward the Kawasaki Daishi temple when they encountered the large retinue of Shimazu Hisamitsu, regent of the Satsuma Domain and father of its daimyo, Shimazu Tadayoshi. The procession was heading south, and it filled the entire width of the road. Richardson and his companions rode along the edge without dismounting. When they reached the main body of the procession, Richardson pushed his horse toward the center. Shimazu's bodyguards gestured repeatedly for him to dismount. He did not. A samurai blade ended the impasse.

The killing exposed a fault line between two incompatible legal worlds. Under Japanese feudal law, samurai held a right called kiri-sute gomen -- permission to strike down anyone of lower rank who showed disrespect. Shimazu's retinue considered Richardson's behavior an intolerable insult. To the Western community in Yokohama, the killing was murder, a violation of the extraterritorial protections guaranteed to foreign nationals under the treaty port agreements. Japanese authorities pointed to Eugene Van Reed, an American who had dismounted and bowed before a daimyo's procession, as proof that respectful behavior was possible. The Western community found Van Reed's deference appalling -- they considered themselves the equals of any Japanese person and expected to be treated accordingly. Richardson's own uncle, upon hearing of his nephew's death, was reportedly unsurprised, blaming the young man's recklessness and stubbornness. Frederick Wright-Bruce, the British envoy to China, called Richardson "an arrogant adventurer."

Britain demanded 100,000 pounds from the Tokugawa Shogunate and 25,000 pounds from the Satsuma Domain specifically, along with the arrest and trial of the samurai who had killed Richardson. The Shogunate eventually paid its share, but the Satsuma refused. In August 1863, eleven months after Richardson's death, the Royal Navy sailed seven warships into Kagoshima Bay and opened fire on the Satsuma capital. The bombardment destroyed much of the city, but the British fleet also took damage and casualties from Satsuma shore batteries. The result was a military stalemate that taught both sides something. The Satsuma, impressed by the power of the Royal Navy, sought a trading relationship with Britain. They paid the 25,000 pounds in compensation -- borrowing the money from the Shogunate's own treasury. They never paid it back. Five years later, the Satsuma helped overthrow the Tokugawa Shogunate in the Meiji Restoration, and the debt died with the old regime.

Namamugi itself is now part of Tsurumi Ward in Yokohama, a quiet residential neighborhood swallowed by the city's postwar growth. The Tokaido road Richardson traveled has been paved, widened, and built over, though its ancient route is still traceable through modern streets. A poetic monument stands at the site, inscribed with a Chinese-style poem by Prince Yamashina Akira. Richardson lies in the Yokohama Foreign General Cemetery, between the later graves of his companions Clark and Marshall, who survived the attack but eventually joined him in the same burial ground. The incident that bears this village's name did not just kill a man or start a war. It became a hinge point in Japanese history -- the moment when the collision between feudal authority and Western treaty rights generated enough heat to melt the structures holding the old Japan together. The Satsuma, who cut Richardson down, would become the architects of the new Japan that rose from the wreckage.