Hatakeyama Kuniuji was Oshu Kanrei (regional deputy) for the Ashikaga shogunate. Together with his father Hatakeyama Takakuni, he administered the Oshu region on behalf of Ashikaga Takauji, based at Iwakiri Castle (also called Takamori Castle). In 1351, when the rivalry between the Ashikaga brothers Takauji and Tadayoshi (the Kanno Disturbance) spread to Oshu, Kira Sadaie, on the Tadayoshi side, attacked Kuniuji's Iwakiri Castle. Kuniuji held out with allies including the Miyagi and Rusu clans in what became known as the Battle of Iwakiri Castle, but was overwhelmed by Sadaie's forces and committed suicide together with his father Takakuni. More than a hundred Hatakeyama retainers are said to have died or taken their own lives in the battle.

A tragic Oshu administrator who remained loyal to Ashikaga Takauji and died fighting at Iwakiri Castle amid the shogunate's internal strife during the Kanno Disturbance.

The Battle of Iwakiri Castle is known as an event illustrating the intensity of internal shogunate conflict in Oshu during the Nanboku-cho period; the castle site, now Takamoriyama Park, remains in Sendai as the battle's setting.