Over 400 years ago, Yoriyasu Kira, the Setagaya castle owner, had a beautiful concubine, Tokiwahime, who was a daughter of Dewa-governor Ohira, the Okusawa castle owner. Tokiwahime had monopolized Yoriyasu’s love upon herself. The ladies-in-waiting who were jealous of it told Yoriyasu the lie of Tokiwahime. Believing that, Yoriyasu gradually moved away from Tokiwahime. Tokiwahime, who was doubted her love to him and was sad, decided to die, and tied a suicide note to her father to the legs of the white egret that she usually had loved, and released. Yoriyasu, who was hunting just in the time, shot down the egret. After seeing Tokiwahime’s suicide note that was tied to the egrets foot and found out the truth, Yoriyasu quickly returned to the castle, but Tokiwahime had already harmed herself. The blood of a dead egret permeated the ground, and the following year, a pure white egret-like flower bloomed. Eventually, people who knew this story came to call the flower the White-Egret.

今から400年以上も昔、世田谷城主の吉良頼康には奥沢城主の大平出羽守の娘で常盤という美しい側室がいました。常磐姫は頼康の愛を一身に集めていました。それを妬んだ側女達が嘘の告げ口を頼康にしました。それを信じた頼康は、常盤姫をだんだん遠ざけるようになりました。愛情を疑われ悲しみにくれた常盤姫は死を決意し、普段から可愛がっていた白鷺の足に父宛の遺書を結び付けて放ちました。丁度狩をしていた頼康がその白鷺を射落としました。足に結びつけられていた常盤姫の遺書を見て真実を知った頼康は急ぎ城に帰りましたが、常盤姫はもう自害した後でした。死んだ白鷺の血が大地に染み込む、翌年そこには純白の白鷺のような花が咲きました。やがてこの話を知った人達がその花をサギソウと呼ぶようになりました。