[5][6] Watanabe began figure skating at the age of three after watching Shizuka Arakawa win gold at the 2006 Winter Olympics on TV.

Watanabe was briefly coached by Mie Hamada until the MF Figure Skating Academy opened in her hometown of Chiba in the spring of 2021.

She then appeared at the Coupe du Printemps at the senior level, winning gold, before placing tenth at the World Junior Championships to conclude the season.

[1] Watanabe began the season by making her Challenger series debut at the 2022 CS Lombardia Trophy, where she unexpectedly won the gold over reigning World and Japanese champion Kaori Sakamoto.

[12] Following her success at the Lombardia Trophy, she was selected to replace Wakaba Higuchi at both of her Grand Prix assignments when the latter withdrew due to an injury.

[13] Making her Grand Prix debut at the 2022 Skate Canada International, she was considered a favourite going in but placed sixth in the short program due to rotation issues on some triple jumps.

[17] She rallied in the free skate, landing a slightly underrotated triple Axel and placing third in that segment, and rose to fifth overall, 5.05 points behind bronze medalist Sumiyoshi.

[25][26] At the World Championships, held on home ice in Saitama, Watanabe placed fifteenth in the short program, but rose to tenth overall with a seventh-place free skate.

On the flight to Vancouver for the 2023 Skate Canada International, her first Grand Prix assignment, she watched Avatar: The Way of Water, whose score was the source of her short program music.

[30] She finished second in the short program at the 2023 Cup of China despite slight underrotation calls on both parts of her jump combination, setting a new season's best score of 65.09.

[33] Despite her national result, she was assigned to the Japanese team for the 2024 Four Continents Championships, where she finished narrowly fourth in the short program, 1.03 points behind American Ava Marie Ziegler in third place, after her jump combination received quarter underrotation calls on both parts.

Going on to compete on the 2024–25 Grand Prix series, Watanabe won the silver medal at 2024 Skate America behind teammate Wakaba Higuchi.

She also said that looking forward to the Japan Figure Skating Championships in December, she hoped to plan a triple Axel in both her short and free programs.