Okabe Masatsuna served as a bushō during the Sengoku and Azuchi-Momoyama periods.  He was a retainer of the Imagawa, the Takeda, and the Tokugawa clans.  Masatsuna also had the name of Jirōuemon-no-jō.  Over the years, Masatsuna served three powerful clans – the Imagawa, the Takeda, and the Tokugawa.

Masatsuna was born as the eldest son of Okabe Hisatsuna, a retainer of the Imagawa clan of Suruga Province.

During his youth, Masatsuna became friends with Tokugawa Ieyasu who was brought to Sunpu as a hostage.  He supported the Okabe family with daily activities and, among the senior retainers of the Imagawa family, exhibited the most friendly attitude toward Ieyasu.

Initially, Masatsuna served the Imagawa family, participating in battle for the first time in 1557.  He made a name for himself by capturing two heads in battle.  Thereafter, the Invasion of Suruga by Takeda Shingen resulted in the loss of the province.  After the decline in the power of the Imagawa, he holed-up in the Imagawa residence and put-up stiff resistance.  Following the demise of the Imagawa clan, he was praised for this bravery in battle and became a retainer of the Takeda clan.

As a retainer of the Takeda, Masatsuna made significant contributions at the Battle of Mikata-ga-hara in the twelfth month of 1572, and at the Siege of Iwamura Castle from 1573 to 1575.  In 1581, the Tokugawa toppled Takatenjin Castle at the Siege of Takatenjin Castle.  After the death in battle of family members including Okaba Motonobu (the chamberlain of the castle), Masatsuna became a retainer of Tokugawa Ieyasu.  In the sixth month of 1582, Oda Nobunaga died in a coup d’état known as the Honnō Temple Incident, whereupon Ieyasu invaded Kai Province.  Masatsuna engaged in activities to lure former acquaintances from among the Takeda retainers to the side of the Tokugawa, supporting the pacification of Kai by Ieyasu.  With respect to the structure established by the Tokugawa for the governance of Kai, there is a theory that Masatsuna held the same status as a hereditary retainer of the Tokugawa known as Hiraiwa Chikayoshi.

The following year, however, he died.  There are various theories concerning the year and causes of his death.  He may have been killed in battle.  Alternatively, he frequently held banquets to lure the former retainers of the Takeda clan, so he may have died from alcohol poisoning.  His grave is at the Hōtai Temple in Sunpu.

Masatsuna’s grandson, Okabe Nobukatsu, a bushō and daimyō in the early Edo period, was rewarded for the contributions of his grandfather, receiving a fief of 60,000 koku in Kishiwada in Izumi Province.