Akechi Mitsutsugu served as a bushi during the Sengoku period.  He was the lord of Akechi Castle (also known as Nagayama Castle) in Mino Province.

In 1468, Mitsutsugu was born as the son of Akechi Yorinao.  He had the childhood name of Chiyojumaru.

As lord of Akechi Castle, Mitsutsugu governed the eastern portion of Mino.  The Akechi family became well-known historically from Mitsutsugu’s generation.  While the Toki clan remained influential in Mino at this time, Mitsutsugu quickly aligned with Saitō Dōsan after Dōsan usurped the Toki clan and became the military governor of Mino.  Mitsutsugu sent his young daughter, Komi-no-kata, as a hostage to the Saitō.  She later became Dōsan’s formal wife, giving birth to Sagiyama-dono (known as Nōhime), who later married Oda Nobunaga.

In 1508, Mitsutsugu was given the title of Junior Fifth Rank (Lower) and Governor of Suruga.  In 1525, he entered a Buddhist monastery, adopting the name of Issekisai Sōzen.