Located in Ryōgoku, Sumida Ward, just west of Ryōgoku Elementary School, lies Honjo Matsusaka-cho Park (本所松坂町公園), a small memorial site for Kira Kōzukenosuke Yoshihisa (吉良上野介義央, 1641-1703), a court official at Edo Castle and infamous villain in the popular story of Chūshingura, the literary account of the incident involving the Forty-Seven Rōnin. Kira's residence, 86 times larger than the current park, was the location of the Genroku Akō incident, in which the 47 rōnin, former retainers of Asano Naganori, the daimyō of Akō, avenged their master's death.
Yoshihisa, daimyō of Mikawa, held the hereditary position of kōke (高家), a master of ceremonies, and resided originally in the Kajibashi District near Edo Castle. After Naganori had been forced to commit suicide rumours had it that former Akō retainers would take revenge, an unsettling prospect to many daimyō living in the neighbourhood. Consequently, Yoshihisa moved his residence to Honjo Matsusaka-cho in September 1701. The Kira Kamiyashiki (吉良上屋敷), Yoshimisa's official residence, was extensive: it measured 132 metres by 62 metres (2,550 tsubo or 8,400 square metres). The front gate was on the east side (nowadays facing Ryōgoku Elementary School), the back gate on the west side. The whole compound was surrounded by a namako wall (海鼠壁 namakokabe, a traditional finish protecting vernacular buildings from water and fire) and nagaya (長屋, traditional longhouses).
Figurine of Kira Yoshihisa
After the attack on January 30, 1703, the house was confiscated by the shogunate. In 1934, local residents of Ryōgoku 3-chome purchased the small piece of land surrounding the well which was allegedly used by the Akō retainers to clean Kira's severed head and donated it to Tōkyō City. In 1950, the land was transferred to Sumida Ward.
Every year on December 14 the attack on Kira's mansion is commemorated in a local "Gishi Festival" in Ryōgoku (not to be confused with the Gishi-sai Festival at Sengaku-ji Temple where the 47 rōnin are buried).
The well where Kira's severed head is said to have been cleaned.
Woodblock print by Katsushika Hokusai (Kanadehon Chûshingura Act XI Jûichidanme, from the series The Storehouse of Loyal Retainers)