The name is romanized both "Izaki" and "Isaki" (伊崎 俊二). The site uses Izaki and most English references use Isaki.
Shunji Isaki was born on 5 February 1892 in Fukuoka Prefecture, on Kyūshū. He graduated from the Imperial Japanese Naval Academy with the 42nd class in 1914, ranked 23rd of 117 cadets.
As a midshipman he served in the cruisers Soya and Kashima. He was commissioned sub-lieutenant on 13 December 1915 and went to the Chikuma and Hirado, but he saw no combat in the First World War. After the war he went back to school for the newest gunnery and torpedo methods, then served in the battleship Yamashiro, the cruiser Yakumo and the battleship Hiei. As a torpedo-specialist lieutenant he served in the light cruisers Yūbari and Sendai. Torpedoes, and the fast light ships that carried them, would shape the rest of his career.
His first command was the destroyer Nara, from 1 November 1926, and he was made lieutenant commander a month later. He went on to command the destroyers Kuri, Ashi, Asanagi, Yūnagi and Shikinami. That is a long run of small-ship commands, the training ground of the night-torpedo tactics the Japanese navy relied on. After his promotion to captain in 1936 he commanded the light cruiser Sendai in 1938, then the heavy cruiser Mogami, the light cruiser Jintsū and the heavy cruiser Maya.
He was promoted to rear admiral on 1 November 1942 and given Destroyer Squadron 2, with his flag in Jintsū, the ship he had once commanded. On the night of 12–13 July 1943 he led the squadron down the Slot toward Kolombangara in the central Solomons. An Allied cruiser and destroyer force under Rear Admiral Walden Ainsworth, which included the New Zealand cruiser Leander, was waiting for him. The Battle of Kolombangara was a Japanese tactical victory: Japanese torpedoes crippled all three Allied cruisers and sank the destroyer Gwin. But Jintsū, leading the column, was caught in the searchlights and the gunfire, and then hit by torpedoes. Her bridge was destroyed and Isaki was killed with most of her crew. He was promoted to vice admiral after his death.
Date flag: Wikipedia gives his death as 12 July 1943, the evening date. The live page lists the battle as 13 July 1943 (the action ran past midnight). Both refer to the same night.
Sources
Wikipedia, "Shunji Isaki" (citing Crenshaw, South Pacific Destroyer; Dull; Hara, Japanese Destroyer Captain; Morison, vol. 6; combinedfleet.com).
Wikipedia, "Battle of Kolombangara" (Allied force, Ainsworth, Leander, cruiser damage, loss of Gwin).
Live Pacific Ships page for this officer.