Matsushita was born on 1 August 2005.[2] He grew up in Utsunomiya, where he attended Yokokawa Nishi Elementary School [jp] and Yonan Junior High School [jp]; he later attended Tochigi Prefectural Utsunomiya Minami High School [jp] in Tochigi.[3][4] He swam for a club in Utsunomiya and later enrolled at Toyo University, where he received training under coach Norimasa Hirai, who also coached Olympic gold medalist Kosuke Hagino, one of Matsushita's favorite swimmers.[4][5]
Matsushita, whose first experience in swimming came at age one, won his first swimming competition in junior high school.[6] In 2022, he competed at the Junior Pan Pacific Swimming Championships and won four medals, including individual medals in the 200m individual medley (silver) and 100m butterfly (bronze).[7] Later that year, he competed at the 2022 FINA World Junior Swimming Championships and won silver in the 200m individual medley.[2] The following year, he was selected for the 2023 World Aquatics Junior Swimming Championships, where he won the gold medal in the 400m individual medley while setting the championship record in the event with a time of 4:10.97.[5][6]
In March 2024, Matsushita became the first Japanese swimmer to qualify for the 2024 Summer Olympics, winning gold at the Japanese Olympic trials in the 400m individual medley while beating out previous Olympic medalists Tomoru Honda and Daiya Seto.[4][5][8] At the Olympics, Matsushita was the youngest participant in the event but reached the finals, where he won the silver medal, only behind gold medalist Léon Marchand of France.[5][9]
