2018–2019

In August 2018, when Honda was 16 years old, he won the bronze medal in the 200 metre butterfly with a time of 1:58.70 and a silver medal in the 4×100 metre medley relay with a final time of 3:41.95 at the 2018 Junior Pan Pacific Swimming Championships in Suva, Fiji.^[4] The following year, at the 2019 FINA World Junior Swimming Championships held in August at Danube Arena in Budapest, Hungary, he won the silver medal in the 200 metre butterfly with a final mark of 1:55.31, sharing the podium with gold medalist Luca Urlando of the United States and bronze medalist Federico Burdisso of Italy.^[5]

2021–2022

Leading up to the 2020 Olympic Games, in April 2021 in Tokyo, Honda was one of two male swimmers to make the Japan Olympic Team in the 200 metre butterfly.^[6] At the 2020 Summer Olympics, held in the summer of 2021 in Tokyo, he finished second in the final of the 200 metre butterfly to win the silver medal with a time of 1:53.73, which was 2.48 seconds behind gold medalist Kristóf Milák of Hungary and 0.72 seconds ahead of bronze medalist Federico Burdisso.^[3][7] The following summer, at the 2022 World Aquatics Championships in Budapest, Hungary, he won the bronze medal in the 200 metre butterfly, this time finishing behind gold medalist Kristóf Milák and silver medalist Léon Marchand of France with a time of 1:53.61.^[8][9] Three days earlier in the Championships, he finished in a time of 4:12.20 in the final of the 400 metre individual medley to place seventh.^[10] On 22 October 2022, he won the gold medal in the short course 200 metre butterfly at the 64th edition of Japan's National Short Course Championships, held in Tokyo, with a world record time of 1:46.85.^[2][11][12]

2023

At the Japan Swim 2023, held in April in Tokyo, Honda won the silver medal in the 400 metre individual medley with a personal best time of 4:10.37.^[13] Two days later, on the third morning, he ranked first in the preliminaries of the 200 metre butterfly with a 1:54.43 and qualified for the final.^[14] In the evening, he won the gold medal with a 2023 World Aquatics Championships and 2022 Asian Games qualifying and personal best time of 1:53.34.^[15][16] The fifth morning, he finished in a time of 52.02 seconds in the preliminaries of the 100 metre butterfly, ranking fourth overall and qualifying for the final.^[17] He equalled his time of 52.02 seconds in the final, placing fifth.^[18]

Long course metres (50 m pool)

Short course metres (25 m pool)

Short course metres (25 m pool)