Yusa Morimitsu served as a bushō during the Sengoku and Azuchi-Momoyama periods. He was a retainer of the Noto-Hatakeyama clan.
Morimitsu was born as the eldest son of Yusa Tsugumitsu. Initially, he received one of the characters in his name from his lord, Hatakeyama Yoshitsuna, adopting the name of Tsunamitsu; however, after the ouster of Yoshitsuna in an event known as the Political Incident of Eiroku 9 in 1566, he changed his name to Morimitsu. There is almost no information concerning his activities during the time that he was named Tsunamitsu.
In 1570, under Hatakeyama Yoshinori (Yoshitsuna’s eldest son), Morimitsu was appointed to serve, along with Chō Tsunatsura, Nukui Kagetaka, Taira Akitomo and others on a council of elders. Morimitsu served in an important role for the Noto-Hatakeyama clan including being in charge of diplomacy with the Uesugi clan, but the timing of his succession to become of head of the family is uncertain and, even after becoming an adult, his father, Tsugumitsu, continued as an important contributor in the diplomatic and political spheres.
In 1577, during the Siege of Nanao Castle, Morimitsu and Tsugumitsu colluded with Uesugi Kenshin, but, after the demise of Kenshin the following year, surrendered to the Oda in the wake of a second invasion by Nobunaga. Nevertheless, owing to the role of Tsugumitsu in the earlier killing of a majority of the Chō family who had been allies of the Oda, Nobunaga refused to forgive them and, in 1581, both Morimitsu and Tsugumitsu were executed. According to one theory, Morimitsu and Tsugumitsu did not surrender but instead fled to Nanao Castle, but after their hide-out was discovered by Chō Tsuratatsu, the whole family was killed.