thumb|250px|Yanagisawa Yoshiyasu
thumb|right|120px|Yotsu-hanabishi or<br>Yanagisawa's Hanabishi,<br> the [[Mon (emblem)|emblem of the Yanagisawa clan]]
was a Japanese samurai and daimyo of the Edo period. He was an official in the Tokugawa shogunate and a favourite of the fifth shōgun, Tokugawa Tsunayoshi. His second concubine was Ogimachi Machiko, a writer and scholar from the noble court who wrote monogatari.
Career
The Yanagisawa house traced descent to the "Kai-Genji," the branch of the Minamoto clan which had been enfeoffed with the province of Kai in the eleventh century.
Yoshiyasu served Tsunayoshi from an early age, becoming his Wakashū and eventually rose to the position of soba yōnin. He was the daimyō of the Kawagoe han, and later of the Kōfu han in Kai Province. This appointment was a signature honour as it has been the fief held by Tsunayoshi before becoming shōgun, and of Ienobu, his heir apparent, as well as having an historic familial connection; he retired in 1709. Having previously been named Yasuakira, he received a kanji from the name of the shōgun, and came to call himself Yoshiyasu. He built Rikugien Garden, a traditional Japanese garden, in 1695. He had an adopted son named Yanagisawa Yoshisato by Tokugawa Tsunayoshi with Yoshiyasu's concubine, Sumeko.
According to the Sanno gaiki, Yanagisawa was a lover of the shōgun, Tokugawa Tsunayoshi, who was reported to have had many relationships with men, and numerous male favourites.
Yanagisawa played a pivotal role in the matter of the forty-seven rōnin.
He was noted for his patronage of a number of scholars, officials, and religious figures, as well as for his own scholarly interests. For instance, he was an early employer and supporter of the influential Confucian scholar Ogyū Sorai.