He was the head of the Nitta clan in the early fourteenth century, and supported the Southern Court of Emperor Go-Daigo in the Nanboku-chō period.
Later, he fought the Ashikaga brothers on the Emperor's behalf in a see-saw campaign which saw the capital change hands several times.
Returning to his home province of Kozuke, Yoshisada rallied the aid of other descendants and vassals, including his brother Yoshisuke of the Minamoto clan, and began to march toward Kamakura through Musashi.
Judging it's impossible to enter by land, Nitta decided to try by sea, bypassing Inamuragasaki Cape on Sagami Bay, west of Kamakura.
Once there, Nitta took advantage of a low tide and moved his men in through the beaches to the south, but according to the Taiheiki, he threw his sword into the surf and prayed to Ryūjin, who parted the waters for him.
[3] Taiheiki states, Dismounting from his horse, Yoshisada removed his helmet and prostrating himself across the distant seas prayed to Ryūjin.
"It is said that the lord of Japan from the beginning, Amaterasu Ōmikami, enshrined at Ise Jingū, hid herself within a Vairocana and appeared as Ryūjin of the vast blue seas.
[4] The stele at Sode no Ura (袖の浦), the tiny bay west of Inamuragaki, says:[5] 666 years ago on May 21, 1333[6] Nitta Yoshisada, judging an invasion on land to be difficult, decided to try to bypass this cape.
He kept up the investment of Akamatsu's strongholds at Shirohata and Mitsuishi until June, when he retreated in the face of advances by Tadayoshi's army.
While Nitta was fighting in the siege of Kuromaru against Hosokawa Akiuji, an ally of Takauji, his horse was felled by arrow fire.