Hashimoto was born in Kyoto as a younger son of a Shinto priest. Hashimoto saw action in many crucial Pacific operations. He was promoted to Lieutenant Commander in 1944. Later in the war, Hashimoto was given command of the Japanese submarine I-58 which sank the USS Indianapolis (CA-35) on 30 July 1945. The sinking of the Indianapolis ultimately cost the lives of 879 of the cruiser's 1,196-man crew the worst single at-sea loss of life in the history of the U.S. Navy. After the war, Hashimoto was brought by the US Navy to testify in the court martial against Captain Charles McVay, commander of the Indianapolis who was convicted for "hazarding his ship by failing to zigzag". At the trial, Hashimoto testified that zigzagging would not have made a difference, for he would have been able to sink the cruiser regardless. Decades later, Hashimoto sent a letter to Senator John Warner as part of an effort to exonerate McVay. Hashimoto spent the final years of his life as a Shinto priest in Kyoto, dying at the age of 91 in 2000.