Kaoru Otsuki (大月薰, Ōtsuki Kaoru, August 6 1888-1970), born in Yokohama, Kanagawa Prefecture, Japan, was the second wife of Sun Yat-sen, founder of the Republic of China.
In 1898, Sun Yat-sen encountered Kaoru in Yokohama's Chinatown. In 1901, Sun requested that Kaoru's father to allow her to marry him, but was refused because of the great age difference between Sun and Kaoru (at the time, Sun was 37 while Kaoru was only 14). One year later, Sun Yat-sen proposed marriage again. In 1903 their wedding ceremony was held in Yokohama. At the time, Sun was still married to his first wife, Lu Muzhen.
In 1906 they had a daughter, Fumiko; however, Sun left Japan before her birth. Kaoru later remarried twice, while Fumiko was adopted by a family surnamed Miyagawa.