Shimada began learning to skate at the age of six years old. He originally trained in his hometown of Matsuyama before moving with his mother to Okayama, the same city where Daisuke Takahashi and Tatsuki Machida would train, when Shimada was around ten years old. There, he trained at the Shujitsu Gakuen Okayama and was coached by Kotoe Nagasawa.[5][6]
At the 2013–14 Japan Championships, Shimada won the gold medal on the advanced novice level and finished seventeenth on the junior level. The following year, he finished second on the advanced novice level and sixteenth on the junior level at the 2014–15 Japan Championships.[7]
2015–2016 season: Junior international debut and Youth Olympics
Although Shimada was assigned to compete at the 2020 Internationaux de France, the event was ultimately cancelled due to the COVID-19 pandemic.[11][12] His only other competition was the 2020–21 Japan Championships, where he finished eighth.[7]
Shimada unexpectedly finished in second place at the 2022–23 Japan Championships, despite a "shaky" landing on his attempted quadSalchow.[13] He was only sixth in the free skate, struggling with a number of jumps, but he remained second overall, less than two points ahead of bronze medalist Kazuki Tomono.[14] Despite being the national silver medalist, the Japan Skating Federation's selection criteria for the 2023 World Championships led to his not being named to one of Japan's three berths, which drew protest from Shimada's friend and training partner, Japanese national champion Shoma Uno. Shimada was instead assigned to compete at the 2023 Four Continents Championships, where he came eleventh.[15][8]
Shimada began the season at the 2023 CS Nebelhorn Trophy, winning the bronze medal.[8] He was invited to participate in the Japan Open as part of the host team, finishing third in the men's event, while Team Japan won gold.[17]
The week before competing at the 2023 Grand Prix de France, Shimada twisted his ankle in practice. He ultimately placed tenth at the event, and said he hoped his ankle would be healed in time for his second Grand Prix event.[18]He went on to finish sixth at the 2023 Grand Prix of Espoo.[19]
Beginning his season by competing on the 2024–25 Grand Prix series, Shimada finished sixth at 2024 Skate America. He would then go on to win his first ISU senior Grand Prix medal, a silver at the 2024 Grand Prix de France.[8] Shimada expressed elation at this result, saying, "I still can’t believe that I am here in the medals. I've worked with Stéphane for such a long time, I appreciate his support so much. I want to thank him dearly for all of put hard work together. Last night he told me “you’re the best”, and put me in a really positive mindset. I was really calm ahead of my skate today and in a really positive mindset."[20]
