[3] Known for his quick and explosive movements with signature drop shots on court, Watanabe, together with Arisa Higashino, had won 2 consecutive bronze medals in the mixed doubles event at the 2020[4] and 2024 Summer Olympics,[5] as well as being four-time BWF World Championships medalists.
[8][9] In June 2014, he made his first appearance in the senior international event at the Japan Open, competed in the mixed doubles with Higashino, but the duo was defeated in the first round.
He captured two titles at the 2014 Korea Junior Open in the boys' and mixed doubles event teamed-up with Mitsuhashi and Chiharu Shida respectively.
In July, he competed at the Asian Junior Championships, clinched the bronze medals in the boys' singles and mixed team events.
[10][11] He reached his first final in the senior international event at the 2015 Russian Open a BWF Grand Prix tournament, where he and his partner Higashino defeated by Chan Peng Soon and Goh Liu Ying.
[19] Besides that, the duo finished in the semi-finals at the Malaysia, Japan, French, and Fuzhou China Opens;[20][21][22][23] and in the year-end tournament BWF World Tour Finals.
[26][27][28] Watanabe also part of the Japanese national team that won the silver medal in the Thomas Cup and the bronze in the Asian Games.
[34] At the Asian Championships, Watanabe and Endo beating the top seeds and current World number 1, Gideon and Sukamuljo with a landslide score of 21–18, 21–3.
[44] Meanwhile, with Endo, their best result were finalists in the World Tour Finals, where the duo failed for the sixth time to beat the Indonesian veteran pair Mohammad Ahsan and Hendra Setiawan in their seven meetings.
[47] Watanabe then made history for Japan badminton, as he and his partner Endo, becoming the first Japanese men's doubles champions at the All England Open, after beating Marcus Fernaldi Gideon and Kevin Sanjaya Sukamuljo in the final.
[49] In March, Watanabe won both the men's and mixed doubles disciplines in the All England Open with Hiroyuki Endo and Arisa Higashino.
Watanabe and Endo's pace was stopped in the quarter-finals to eventual gold medalists Lee Yang and Wang Chi-lin, while in the mixed doubles, Watanabe and Higashino clinched a bronze medal after winning the bronze medal game against Tang Chun Man and Tse Ying Suet in straight games.
[51][52] Since Endo decided to retire from international tournaments after the Tokyo Olympics, Watanabe has focused on competing in mixed doubles.
[65] In the following week, they emerged as a champion in the India Open, after their opponent Wang Yilyu and Huang Dongping withdrawn from the final match.
[66] In March, they unable to defend their All England Open title, since Watanabe struggling with injury in the second round against Kim Won-ho and Jeong Na-eun.