[7] He captured a title at the 2014 Korea Junior Open in the boys' doubles event teamed-up with Watanabe.

Mitsuhashi started the 2015 season, by winning the boys' doubles title at the Dutch Junior tournament with Watanabe.

He participated at the Asian Junior Championships, clinched the bronze medal in the mixed team events.

In November, he won the boys' doubles bronze medal at the World Junior Championships in Lima, Peru.

In September, he won the Vietnam Open, marking his first BWF World Tour title.

At the Japan Masters in November, they defeated world number 9 Mohammad Ahsan and Hendra Setiawan in straight games in the first round.