During his early years Sadayo was taught Buddhism, Confucianism and Chinese, archery, and the military arts such as strategy and horse-back riding by his father (governor of the Tōkaidō provinces Tōtōmi and Suruga), along with poetry, which was to become one of his greatest passions.
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His father, Imagawa Norikuni, had been a supporter of the first Ashikaga shogun, Ashikaga Takauji, and for his services had been granted the position of constable of Suruga province (modern-day Shizuoka prefecture).
Jeong Mong-ju was dispatched to Japan to deal with the problem, and during his visit Kyushu governor Imagawa Sadayo suppressed the early wokou, later returning their captured property and people to Korea.