Lifespan: Bunki 3 (1503) to 8/1 of Eiroku 2 (1559)
Other Names: Rokurō (childhood)
Rank: bushō, sengoku daimyō
Title: Chief of the Left Division of Outer Palace Guards
Father: Yūki Masatomo
Siblings: Masanao, Masakatsu, Oyama Takatomo, sister (wife of Utsunomiya Hisatsuna)
Children: Akitomo, Kotōhime (wife of Mizunoya Masamura)
Adopted Children: Harutomo (third son of Oyama Takatomo)
Yūki Masakatsu served as a bushō and sengoku daimyō during the Sengoku period. Masakatsu was the sixteenth head of the Yūki clan of Shimōsa Province.
In 1503, Masakatsu was born as the son of Yūki Masatomo, the fifteenth head of the Yūki clan.
Under traditional theory, in 1527, Masakatsu inherited the headship of the clan from his father, but, under a more recent theory, Masakatsu’s older brother, Yūki Masanao, succeeded his father as head of the clan around 1532, early in the Tenbun era.
After inheriting the clan, similar to his father, Masakatsu adopted policies to actively promote the expansion of territory, generating frequent disputes with the Satake, the Oda, and the Shimotsuke-Utsunomiya clans. Masakatsu joined forces with Hōjō Ujiyasu to take by force Oguri Castle in Hitachi Province from the Utsunomiya clan. At the Battle of Ebigashima, he defeated Oda Ujiharu, expanding his territory from Shimōsa to Shimotsuke, and beyond to Hitachi. In 1539, during an internal conflict between Nasu Masasuke and his eldest son, Nasu Takasuke, Masakatsu supported Takasuke and fought against the Satake, the Oda, and the Utsunomiya. Traces of these events, however, are said to be attributable to his father, Masatomo, after his retirement. In 1547, following the death of Masatomo, Masakatsu was attacked by Utsunomiya Hisatsuna, but repelled him.
The greatest achievement of Masakatsu was, more so than an expansion of territory, the enactment of well-known provincial ordinances known as the New Laws of the Yūki Clan. Enacted in 1556, these laws stipulated detailed provisions extending as far as the topics of dining and clothing. Viewed as innovative, the rules also covered punishments and so forth for arguments or disputes.
Masakatsu was not blessed with a successor. In 1548, his only natural son, Yūki Akitomo, preceded Masakatsu in death by illness from smallpox, just one day after Akitomo succeeded him as the head of the clan. Meanwhile, Masakatsu wed his daughter, Kotōhime, to Mizunoya Masamura, but she died soon after giving birth to a daughter. As a result, Masakatsu adopted Harutomo, the third son of his younger brother, Oyama Takatomo, to become his successor. In his latter years, Masakatsu entered the priesthood, but suffered from illness and, after a counterattack by Oda Ujiharu, lost a portion of his territory.
On 8/1 of Eiroku 2 (1559), Masakatsu died at the age of fifty-seven. He was succeeded by his adopted son, Yūki Harutomo. There are alternative theories as well.
Masakatsu was known for being a skillful artist, frequently painting self-portraits and other subjects. One of his self-portraits dated 1552 is at the Daiun Temple in Ibaraki Prefecture.