Teranishi Naotsugu served as a bushō and daimyō during the Azuchi-Momoyama period.  He was the lord of Honda Castle in Mino Province.  In the early Edo period, Naotsugu served as a chief retainer for the Kaga domain.  He was a hereditary retainer of the Toyotomi family, but after the Battle of Sekigahara, was removed from his position and became a retainer of the Maeda clan.  Naotsugu was the younger cousin of another chief retainer of the Kaga domain named Teranishi Hidenori.

In 1557, Naotsugu was born as the son of Teranishi Suruga-no-kami, a retainer of Hashiba Hideyoshi (later known as Toyotomi Hideyoshi).  According to historical accounts of Owari, he was from the village of Banba in the Kaitō District of Owari.

Similar to his father, Naotsugu served Hideyoshi and was awarded Honda Castle in the Motosu District of Mino.  Around 1590, Naotsugu was appointed as the official representative of the Toyotomi to manage land held directly by the Toyotomi family with a yield of 100,000 koku in Nagahama in Ōmi Province.

In 1593, during the Bunroku Campaign, Naotsugu was stationed in Nagoya Castle in Hizen Province leading 200 men as a member of the rear guard.  He was then invested with the title of Junior Fifth Rank (Lower) and Governor of Bitchū.  In the spring of 1595, when sharing responsibilities for the construction of Fushimi Castle for Hideyoshi, he already held a fief of 10,000 koku.

After the death of Hideyoshi in the eighth month of 1598, Naotsugu received as a keepsake a precious sword manufactured by Hōshō Gorō Sadamune, one of five renowned schools of sword-making from the late Kamakura period.

In 1600, Naotsugu had landholdings in Ise, Ōmi and Echizen provinces totaling 10,000 koku (or 10,014 koku).  In the months leading up to the Battle of Sekigahara, Naotsugu, together with Ujiie Yukihiro (the lord of Kuwana Castle in Ise Province) deployed for the Conquest of Aizu.  While en route, after learning that Ishida Mitsunari had launched a rebellion, they returned to Kuwana Castle.  Yukihiro rejected offers to join either side, declaring a neutral position, but after the Western Army reached Ise, he and Naotsugu joined the Western Army, holing up in the castle along with Yukihiro’s younger brother, Ujiie Yukitsugu.  After the Battle of Asainawate, a unit from the area owned by Naotsugu in Echizen joined Okuyama Masayuki and Ueda Shigeyasu as reinforcements for the return of Niwa Nagashige to Komatsu Castle.

On 9/17, the day after the Western Army was defeated at the main Battle of Sekigahara, upon the advice of Yamaoka Kagetomo, he surrendered and vacated his castle.  The landholdings of the Teranishi family were seized and he was removed from his position.

Naotsugu underwent the rites of tonsure, adopted the monk’s name of Ikan, and drifted.  Owing to the generosity of Maeda Toshinaga, in 1601, he was engaged in service to the Maeda family in the Kaga domain.  At this time, Naotsugu was granted a stipend of 1,500 koku in the village of Tsumugi in the Kashima District of Noto Province.

In 1649, Naotsugu died at the age of ninety-three.  He was succeeded by his second son, Teranishi Naotake.