As midshipman, Isaki served on the Soya and Kashima. After his commissioning as sub-lieutenant on 13 December 1915, he was assigned to the Chikuma and Hirado, but did not participate in any combat operations during World War I.
After the war, he returned to school to study the latest techniques in naval artillery and torpedo warfare, and subsequently served on the Yamashiro, Yakumo and Hiei. As a lieutenant specializing in torpedoes, he then served on the Yubari and Sendai.
His first command was the destroyerNara from 1 November 1926. Promoted to lieutenant commander a month later, he subsequently was captain of the Kuri, Ashi, Asanagi, and Yūnagi, and Shikinami. After his promotion to captain in 1936, he was reassigned to command the Sendai in 1938, followed by the Mogami, Jintsu, and Maya.
Isaki was promoted to rear admiral on 1 November 1942.
He commanded a destroyer squadron, DesRon2 from his flagship Jintsu during the Battle of Kolombangara against the Royal New Zealand Navy and the United States Navy on 12 July 1943. Although the battle was a victory for Japan, Jintsu was hit repeatedly by gunfire and torpedoes, destroying its bridge and killing Isaki.
Crenshaw, Russell Sydnor (1998). South Pacific Destroyer: The Battle for the Solomons from Savo Island to Vella Gulf. Naval Institute Press. ISBN1-55750-136-X.
D'Albas, Andrieu (1965). Death of a Navy: Japanese Naval Action in World War II. Devin-Adair Pub. ISBN0-8159-5302-X.
Lacroix, Eric; Linton Wells (1997). Japanese Cruisers of the Pacific War. Naval Institute Press. ISBN0-87021-311-3.
Kilpatrick, C. W. (1987). Naval Night Battles of the Solomons. Exposition Press. ISBN0-682-40333-4.
McGee, William L. (2002). "Operation TOENAILS". The Solomons Campaigns, 1942-1943: From Guadalcanal to Bougainville--Pacific War Turning Point, Volume 2 (Amphibious Operations in the South Pacific in WWII). BMC Publications. ISBN0-9701678-7-3.