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.

He had taken religious vows when the Ashikaga bakufu called upon him to travel to Kyūshū and assume the post of constable of the region in 1370 after the failure of the previous constable to quell the rebel uprisings in the region, largely consisting of partisans of the Southern Court supporting one of the rebellious Emperor Go-Daigo's sons, Prince Kaneyoshi.

Sadayo's skill as a strategist was obvious, and he moved rapidly through northern Kyūshū with a great deal of success, bringing the region under his control by October 1372.

In 1400 Sadayo was once again questioned by the Bakufu, this time in relation to the Imagawa's province of Tōtōmi's failure to respond to a levy issued by the Bakufu—a negligence interpretable as treason and rebellion.

Even though Sadayo is better known for his criticism of the more conservative poetry styles, the Nijo school in particular, and his tutoring of Shōtetsu (1381–1459), who would become one of the finest waka poets of the fifteenth century, than he is for his own output, it nonetheless provides a glimpse into the mind of this medieval scholar and his travels.

Sadayo was active in the poetic disputes of that day,[1]: 113–115  scoring a signal victory over the Nijō adherents close to the Ashikaga Shogunate at the time with 6 polemical treatises on poetry he wrote between 1403 and 1412, defending the Reizei's poetic doctrine and their cause (despite Ryōshun's renga poetry's debt to Nijō Yoshimoto's (1320–1388) examples and rules of composition).

With the aid Ryōshun afforded him, Fujiwara no Tanemasa's politicking eventually succeeded in converting the Shogun, ending the matter- until the rival Asukai poetic clan revived the dispute, that is.