Yūki Yoshiaki served as a bushō during the Azuchi-Momoyama and early Edo periods.  He was the eleventh head of the Shirakawa-Yūki clan.

Yoshiaki was born as the lineal heir of Yūki Harutsuna, the tenth head of the Shirakawa-Yūki clan.  When Harutsuna died of illness, Yoshiaki was only seven years old so a family member, Komine Yoshichika, served as his guardian.  In 1574, the Satake clan toppled an auxiliary site known as Akadate Castle in addition to other outlying castles.  Eventually, the Satake captured the main base of the Shirakawa-Yūki at Shirakawa Castle.  Only Sekiwaku Castle continued to be held by Yoshichika.  Owing to the precarious circumstances, Yoshiaki temporarily moved to Nasu but through the mediation efforts of several temples, a settlement was reached with the Satake clan.

In 1575, when Yoshiaki was absent from Shirakawa Castle for an event to mark the beginning of the spring planting season, the castle was captured by Yoshichika and his senior retainers while Yoshiaki was banished from his position.  With the assistance of his chief retainers including Sato Iwami-no-kami and Sato Tosa-no-kami (father and son), Kashiwagi Hayato, and Oshi Ukyō-no-jō, Yoshiaki was harbored at the Tajima house and then fled for protection under the head of the Yanaizu-Kokūzō Temple in Aizu.  In 1582, Yoshiaki, through the offices of Ashina Moritaka, returned to the territory of Shirakawa.  Yoshichika returned a portion of Yoshiaki’s landholdings to him but he resided at the Iwakubo-Kirigishi Castle in Odagawa and did not regain his position as the head of the Shirakawa-Yūki clan.

In a bid to regain the position as head of the clan, Yoshiaki secretly plotted to eliminate Yoshichika.  A jointly sealed covenant circulated among the retainers but owing to the conduct of the Oushū Retribution by Toyotomi Hideyoshi in 1590, the landholdings of Yoshiaki and Yoshichika were seized so Yoshiaki could not follow-through on his plans.  Later, Yoshiaki, along with his son, Tomotsuna, and former retainers, engaged in farming in Ōtagawa.

In 1613, Yoshiaki died at the age of forty-seven.