Shirai first boxed in elementary school, during a mock match-up against a kangaroo at a local carnival. He became interested in boxing afterwards, and made his professional debut in 1943, during World War II. He won his first eight professional fights before being drafted to join the Imperial Japanese Navy. After being released in 1945, he returned to boxing, but was almost forced into retirement because of injuries he had sustained during the war. However, he met Alvin Rober Cahn, a Jewish-AmericanSCAP employee, who became his trainer and manager. Shirai's boxing skills improved dramatically under Cahn's guidance, and the two formed a close bond. Shirai fought with the aggressive boxing style typical of the Japanese boxers of the time, but made a change to a more technical, defensive style under the guidance of his new trainer. Cahn made Shirai live in his house, and supervised everything from his health and training to his meals. Cahn began to suffer from dementia in his old age, and it was Shirai's family that took care of him. Cahn had no children when he died, and left Shirai with his entire fortune.
Professional career
Shirai won his first fight after teaming with Cahn on July 30, 1948, and won the Japanese flyweight title in 1949. He also won the Japanese bantamweight title the same year, and held both titles for over 3 years, making 5 total defenses. He fought flyweight world championDado Marino on May 21, 1951, in a non-title match. Shirai lost by split decision but fought Marino again in December, 1951, to mark a 7th round KO win. On May 19, 1952, he met Marino for the third time for the world flyweight title. Shirai won by 15 round decision, becoming the new world champion, and first ever Japanese boxer to win a world title. Shirai made four defenses of the world title before losing his title to Pascual Perez in November, 1954 by unanimous decision. He fought Perez again in May, 1955, but lost decisively by KO in the 5th round. He announced his retirement after this loss. His professional record was 48-8-2.
Post retirement
Shirai worked as a boxing commentator and critic before creating a sports gym in 1995 with former world champion Yoko Gushiken. He received an award from the Japanese government in 1995 for his efforts in boxing. He was inducted into the Ring Magazine hall of fame in 1977.
