Ii Naohira served as a bushō during the Sengoku period.  He was a retainer of the Imagawa clan.  Naohira was the sixteenth head of the Ii clan who were kokujin, or provincial landowners, in Tōtōmi Province.  Naohira was the great-grandfather of Ii Naotora and Ii Naomasa.  According to one theory, he was the maternal grandfather of Tsukiyama-dono, the formal wife of Matsudaira Motoyasu (later known as Tokugawa Ieyasu).  As such, he was the great-grandfather of Matsudaira Nobuyasu.

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In 1479 or 1489, Naohira was born as the son of Ii Naouji, the lord of Iinoya Castle.  In 1507, Naohira donated approximately three-quarters of an acre of fields to the Jijō Temple, the family temple of the Ii located in the birthplace of Ii Tomoyasu, the founder of the Ii clan in the Heian period.  He invited 黙宗瑞淵 to Iinoya and changed the name from the Jijō Temple to the Ryōtan Temple.  In 1511, he granted land to Hōda Sukeshirō and informed Hōda Negi, the priest at the Hashisaki Shrine.

Among Naohira’s children, he was preceded in death by his eldest son (Ii Naomune), his second son (Ii Naomitsu), his fourth son (Ii Naoyoshi), and his fifth son (Ii Naomoto).  In 1542, Naomune was killed in an attack at Tahara Castle in Mikawa Province.  Naomitsu and Naoyoshi were killed by Imagawa Yoshimoto following slander by a chief retainer named Ono Masanao in 1545.  Naomoto died of illness in 1541.  After the death of Naomune, his lineal heir, Ii Naomori, became the head of the clan and governed Iinoya.  In 1560, he followed Yoshimoto on a westward march and was killed in a surprise attack by the Oda army at the Battle of Okehazama in Owari Province.

After the demise of Naomitsu, his lineal heir, Ii Naochika, fled for safety to the territory of the Takeda clan in Shinano Province.  In 1555, taking advantage of the death of Ono Masanao, Naochika returned to Iinoya and, after the death of his adoptive father, Naomori, inherited the headship of the Ii clan.  At the time, kunishū across Tōtōmi rebelled against the Imagawa clan in an event known as the Enshū Discord.  Based on slander by Ono Michiyoshi (the son of Masanao), Naochika was suspected by Imagawa Ujizane of colluding with Matsudaira Motoyasu (later known as Tokugawa Ieyasu).  Through the offices of a relative named Niino Chikanori, while traveling to Sunpu to apologize, on either 12/14 (or 3/2) of Eiroku 5 (1563), Naochika was attacked and murdered by Asahina Yasutomo, a senior retainer of the Imagawa, at the Kake River.  He was twenty-eight years old.

Naochika’s lineal heir, Toramatsu (later known as Ii Naomasa) was still in his youth so, in 1563, Naohira became his guardian.  On 9/18 of Eiroku 6 (1563), upon orders of Imagawa Ujizane, Naohira served in the vanguard of an attack against Amano Kageyasu and Amano Motokage (father and son) at Yatsushiroyama Castle following their defection from the Imagawa.  Naohira was killed in action.  He was either seventy-five or eighty-five years old.  Naomori’s daughter, Jirō-Hōshi (Ii Naotora), who had been in the priesthood inherited the headship of the clan.  After living as a wandering samurai, Toramatsu (Ii Naomasa) became the head of the clan in lieu of Naotora and served the Tokugawa clan.  Later, he was counted among the Four Divine Kings of the Tokugawa.

Theories of his demise

In the Ii family records, Imagawa Ujizane launched a battle against Oda Nobunaga to avenge the earlier loss of his father at the Battle of Okehazama.  Naohira deployed with Ujizane.  Naohira’s forces set-up a base at Shirasuka, but a strong wind from the south caused the outbreak of a fire that burned down settlements in the local area.  After the incident, Naohira was suspected of setting a fire at Shirasuka (the thirty-second station along the Tōkaidō connecting Edo and Kyōto) to undermine the rear of the army owing to his anger stemming from the murder of Naohira’s grandson, Ii Naochika, upon orders from Ujizane.  Naohira explained that the fire was caused by unforeseen circumstances, but to assign fault, Ujizane ordered a retainer named Amano Zaemon-no-jō to subdue Naohira who had served as the lord of Iinoya Castle.  While Naohira was making preparations, Otazu-no-kata, the wife of a chief retainer named Inoo Tsuratatsu, offered him poisoned tea.  Later, he fell from his horse and died from the side effects of the poison.

In another section of the Ii family records, Tsuratatsu offered the poison to Naohira who died from the side effects.  Other theories of his demise include that he was killed in a surprise attack by enemy forces or died of illness.  After his death, a subordinate named Ōishi Sakuzaemon carried his body by horse to his hometown of Kawana and martyred himself.

According to records of the Ii family, he is referred to in records of the Tokugawa as Ii Buzen-no-kami so many military chronicles refer to him as Ii Buzen-no-kami.  Ii Naohira was of advanced age so, during deployments, Inoo Tsuratatsu deployed as a proxy for Naohira so Naohira was referred to as Ii Buzen-no-kami.  The achievements of Inoo Tsuratatsu as noted in records of the Ii family are attributable to Naohira.