Sakakibara Yasumasa was born in the year Tenmon-17, the second son of Sakakibara Nagamasa, in the Ueno district of Mikawa Province. The Sakakibara were hereditary retainers of the Matsudaira clan, classified as fudai. However, they did not serve the clan directly, but instead served one of its senior retainers, which at that time was Sakai Tadanao. The young Yasumasa interacted with Matsudaira Motoyasu often from a young age, and was soon appointed his page. Due to his valor in the suppression of the Ikkō-ikki uprising in Mikawa, he was allowed to use the "yasu" from Ieyasu's name. At this time, he unseated his brother and became head of the Sakakibara clan. There are two explanations for this. One is that his brother had been an ally of the Ikko Ikki rebels, and the other is that his brother was a retainer of Ieyasu's son Matsudaira Nobuyasu, who was implicated in what was most probably a non-existenttreason plot against Oda Nobunaga.
Service under Ieyasu
In Eiroku-9, at age 19, Yasumasa had his coming-of-age ritual, and soon after, he and Honda Tadakatsu were made hatamoto by Ieyasu, and each granted command of 50 cavalrymen. From that point on, they would function as Ieyasu's hatamoto unit commanders. Yasumasa battled at Anegawa in 1570, Mikatagahara in 1573, along with the Nagashino in 1575. When Ieyasu chose to defy Toyotomi Hideyoshi, Yasumasa still served under Ieyasu, suggesting the region of Komaki would be suitable for the ensuing campaign. Yasumasa was given the title of "'Shikibu-Shō'", when accompanying Ieyasu to Osaka to meet with Hideyoshi. After the Tokugawa moved to the Kantō region, he was to have a team responsible for the allocation of fiefs. While Ieyasu was serving as one of Hideyoshi's staff in Kyūshū, Yasumasa was to supervise Kantō, as one of the chief administrators.
Later life
Yasumasa received the 100,000 koku fief of Tatebayashi han following the Tokugawa victory at the Battle of Sekigahara, which remained in the family for a few generations. Yasumasa himself died in 1606, at the age of 59, and is buried at Zendoji Temple in Tatebayashi, where his grave still stands.
