Nishiyama made her international debut at the 2023 City of Jesolo Trophy.[1] She advanced into the all-around final at the 2023 All-Japan Championships and placed 12th.[2] She then finished 16th at the 2023 NHK Trophy.[3] At the 2024 DTB Pokal Team Challenge, she won a silver medal in the junior team competition,[4] and she placed seventh in the all-around. She also advanced into the uneven bars final, finishing fifth.[5] She won a bronze medal on the balance beam at the 2024 All-Japan Event Championships, behind seniors Kaoruko Takezawa and Urara Ashikawa.[6]
Nishiyama finished eighth in the all-around at the 2025 All-Japan Championships.[7] She then finished sixth all-around at the 2025 NHK Trophy.[8] At the 2025 All-Japan Junior Championships, she won the all-around silver medal, behind Haruka Nakamura.[9]
In November 2025, Nishiyama competed at the 2025 Junior World Championships. She helped the Japanese team win a silver medal with a score of 107.930, finishing behind France,[10] and she advanced into the all-around final in second place.[11] Individually, she won a gold medal on floor exercise with a score of 13.533, and a silver medal on the vault with a score of 13.633, finishing behind team USA's Lavi Crain.[12][13] In the all-around final, she won a bronze medal with a score of 53.066, finishing behind teammate Yume Minamino and France's Elena Colas.[14][15]
Japan
Japan
