Nagai Naoyuki (永井 尚志?, December 21, 1816 – July 1, 1896), also known as Nagai Genba (永井 玄蕃?) or Nagai Mondonoshō (永井 主水正?), was a Japanese samurai and Tokugawa retainer during the Bakumatsu and Meiji periods.
His great-great-grandchild was Yukio Mishima. Naoyuki's adopted son, Iwanojō Nagai, was the father of Natsu, who was Mishima's grandmother. Iwanojō's real father was Nagasumi Miyoshi (Miyoshi clan) who was a Tokugawa retainer.
Read more about Nagai Naoyuki: Early Life, Career, Tenure As Hakodate Magistrate, Later Life