Long before Tokugawa Ieyasu entered Edo, a family feud within the Uesugi clan, which wielded power in the southern Kanto region, led to the "Battle of Edo in Two (the Battle of Egotahara and Numabukuro)" between Toyoshima Yasutsune and Ota Dokan.
　As a result, Toyoshima Yasutsune, who had previously ruled the northwestern part of Tokyo, disappeared from history. However, a different legend remains in his hometown of Nerima Ward.
　According to this legend, Toyoshima Tsuneyasu, realizing he had no chance of winning, donned dazzling armor and helmet, mounted a white horse with a golden saddle, and committed suicide by drowning in Sanboji Pond. 　(Nihedon @ KesaranPasaran Lab)

Historically, after the Battle of Egotahara and Numabukuro, Toyoshima Yasutsune, whose Shakujii Castle was burned down, fled to Hiratsuka Castle (Kita Ward, Tokyo), and then apparently disappeared after fleeing towards Adachi.

However, this wasn't satisfactory for the locals. They must have had a strong desire to "make their lord's end more glorious in history," and it was against this backdrop that the "Legend of the Golden Saddle" was born.

Edo period documents reportedly state that "on clear days, a golden saddle could be seen shining at the bottom of Sanboji Pond." Typical of Edoites, they didn't miss a beat!

Furthermore, there's a legend that Yasutsune's daughter, Teruhime, followed in her father's footsteps and threw herself into Sanboji Pond. Even today, the "Teruhime Festival" is held in her memory. Every year, a procession of about 100 people, including Teruhime, Toyoshima Yasutsune, and his wife, is selected through open auditions and public recruitment for the "Teruhime Procession," and a stage play, "The Legend of Teruhime," is performed.