Oyamada Toramitsu served as a bushō during the Sengoku period.  He was a retainer of the Kai-Takeda clan, originating from the Ishida-Oyamada clan.

In certain historical accounts, he is referred to as Masatatsu, but his real name from historical documents has been confirmed as Toramitsu.  After entering the priesthood, he adopted the name of Gen’i.  He also had the names of Uehara Iga-no-kami and Oyamada Bitchū-no-kami.  His sons were Oyamada Masayuki and Oyamada Daigaku-no-suke.

The Oyamada clan were hereditary chief retainers of the Takeda family and district landlords in Kai Province, but Toramitsu came from a separate lineage called the Ishida-Oyamada.  Owing to their landholdings in the location of Ishida, the clan adopted the surname of Ishida-Oyamada.

Toramitsu was born as the son of Oyamada Bitchū-no-kami (his father’s real name is unknown).  The family passed-down the informal title of Bitchū-no-kami for generations.  In 1540, after capturing Kaizu Castle, the name of Bitchū-no-kami appears along with Itagaki Nobukata as a chamberlain of the castle.  He contributed to repelling a counterattack by Murakami Yoshikiyo but, in 1552, at the Battle of Shinano Jizō-Tōge, was killed in action.

It is unclear whether Toramitsu was his first name, but, early on, he adopted the name of Uehara Iga-no-kami.  In one account, he commanded a battalion of 70 soldiers.

In the era of Takeda Harunobu (Shingen), the Takeda committed to a full-scale invasion of neighboring Shinano Province.  In the fifth month of 1546, the Takeda forces toppled Uchiyama Castle in the Saku District defended by Ōi Sadakiyo.  Toramitsu first appears in historical accounts from the seventh month of 1546 in reference to the appointment by Harunobu of Uehara Iga-no-kami (Toramitsu) as the chamberlain of Uchiyama Castle.  It is noted that he secured the Saku District which served as a gateway to western Kōzuke Province.

According to one account, in 1548, during an assault against Maeyama Castle in the Saku District, Toramitsu, as the commander of ashigaru, or foot soldiers, deployed under the command of Lord Saburō.  While not clear from genealogical records, Lord Saburō refers to a family member of the Takeda who appears in records from 1550 to 1551.  Owing to use of the name of Saburō Yoshinobu, he may have been a descendant of Yasuda Yoshisada, a bushō from the Kai-Genji of the late Heian period.

On 3/29 of Tenbun 20 (1551), the chamberlain of Uchiyama Castle reverted to the former lord, Ōi Sadakiyo, and Toramitsu returned to Kōfu in Kai.  On 9/20, Sadakiyo was replaced and Toramitsu became the chamberlain of Uchiyama Castle again.  He inherited the Ishida-Oyamada clan and called himself Oyamada Bitchū-no-kami.

To counter an alliance between the Murakami and the Ogasawara serving as military governors of Shinano, in the first month of 1553, Harunobu had Toramitsu send a letter in his own writing to spread misinformation regarding the renovation of Toishi Castle to conceal a deployment to assault Katsurao Castle which served as the main base of the Murakami.  Toramitsu also served as a go-between with Sanada Yukitaka, a member of the kunishū, or provincial landowners, in Shinano and engaged in military operations with Yukitaka.

In the seventh month of 1554, Toramitsu, along with Obu Toramasa, was stationed again at Uchiyama Castle to monitor Murakami Yoshikiyo.

In 1558, Toramitsu was afflicted with a serious illness and barely survived.  A letter from Takeda Harunobu orders Yamamoto Kansuke to pay a visit to wish well a veteran of the family named Oyamada which is believed to be a reference to Toramitsu.

Around 1564, he entered the priesthood and adopted the monk’s name of Gen’i.  In the second month of 1567, recognition was given to the transfer of his fief and troops to his eldest son and designated heir, Masayuki, so Toramitsu is presumed to have retired around this time.  In the eighth month, Toramitsu’s name does not appear in a written pledge made to the Ikushima-Tarushima Shrine.  Thereafter, Masayuki is called Bitchū-no-kami.

Toramitsu last appears in a sealed license from the Takeda family dated in 1572.  According to records from the Rengejō Temple on Mount Kōya, he died on 10/12 of Tenshō 7 (1579) and, until his death, served as the chamberlain of Uchiyama Castle.

According to one chronicle, none of the castles built by Oyamada Bitchū-no-kami were toppled and there is a story that, when building new castles, Takeda Shingen regularly had Toramitsu enter.  He is noted as dying in 1552 at the Battle of Shinano-Tsuneta.  Based, however, on documents dated after this time, this is believed to be a reference to his father who used the same common name of Bitchū-no-kami.  Under another theory, during the Conquest of Kōshū in 1582, Toramitsu, along with Nishina Morinobu, was killed in action at Takatō Castle.  This, however, appears to be in error and instead a reference to his son.

His descendants served as retainers of the Sanada family and as assistant chief retainers of the Matsushiro domain.