Omiya Incident (近江屋事件)

The Omiya Incident occurred at the end of the Edo period during the last days of the Tokugawa shogunate, on December 10, 1867 (November 15 according to the old calendar) when Ryoma SAKAMOTO and Shintaro NAKAOKA were killed at Omiya, the home of Shinsuke IGUCHI in Kawara-machi, Kyoto Prefecture.
It is said that the killing was the deed of the Kyoto Mimarwarigumi (a group for the security of Kyoto)

Details

On November 3, Ryoma moved out of Ikedaya, which the government had had an eye on, and into Omiya. On November 13, Kashitaro ITO visited Ryoma and told him that he was being targeted by the Shinsengumi and recommended that he move to the residence of the Tosa Clan in Sanjo, which Ryoma declined.

In the late afternoon of November 15, Nakaoka visited Omiya and they talked about the Sanjo-ohashi Seisatsu Incident. At night, a man came to Omiya, saying that he was from Totsukawa Village and wished to see Ryoma. Tokichi YAMADA, a former sumo wrestler, was about to show the visitor and his companions when he was attacked from behind (he died the next day). Hearing Yamada's scream, Ryoma yelled out "Hotaena! (Be quiet)" which revealed where he was to the assassins. The assassins ran up the stairs without a sound, opened the sliding door and entered the room.
At this time Ryoma had his forehead slashed (there are other theories, one saying that the assassins gave their name cards before attacking.)
While Ryoma was losing consciousness, he called out "Ishikawa, where's the sword" so as not to reveal Nakaoka's real name. Then he was stabbed in several places, including his chest and died. Nakaoka was still alive and sought help, but he died two days later.

Who were the executioners?

At the beginning, because the assassins were talking in Iyo dialect, it was thought that the deed was done by Sanosuke HARADA and Kuwajiro OISHI of the Shinsengumi (a group who guarded Kyoto during the end of Tokugawa Shogunate). In fact, Kuwajiro OISHI was killed for Ryoma's assassination. In another account, it was thought until the Meiji period that the assassination had been carried out by the Shinsengumi and because of the Ikedaya Incident, the Shinsengumi was fully purged during the Boshin Civil War.

After the start of the Meiji period, Nobuo IMAI, who was a member of the Kyoto Mimawarigumi, confessed to killing Ryoma; however, truth of the matter remains uncertain.

There are many unanswered questions to this incident, with theories other than Imai assassinating Ryoma, including a theory holding that the assassination was by feudal retainers or warriors of Satsuma and another interpretation by Jiro ASADA in his "Mibu Gishin Den"
There are also many who believe that it was the deed of Satsuma, aiming to overthrow the shogunate by force, which is the opposite to the peaceful approach taken by the Kaientai (an association of masterless samurai organized by Ryoma SAKAMOTO) and the Rikuentai (an association of masterless samurai organized by Shintaro NAKAOKA).