[2][3] Yaegashi finished his amateur career with a record of 56–14 after winning the Inter-High School Championship and the National Sports Festival of Japan.
[2] In his first world title shot against the WBC mini-flyweight champion Eagle Kyowa at the Pacifico Yokohama in June 2007, Yaegashi lost for the first time by a wide points margin after suffering a broken TMJ[2] in two places due to an accidental headbutt in the second round.
[10] On June 20, 2012, in a match that marked the first time two Japanese fighters had met to unify world titles, he lost to the WBC champion Kazuto Ioka via a unanimous decision at the Bodymaker Colosseum.
[15][16] Yaegashi returned to the ring in a light-flyweight bout at the Korakuen Hall on January 5, 2013, to knock out Saenmuangloei Kokietgym in the ninth round.
[19][20] On 12 August 2013, Yaegashi successfully defended his title by defeating Mexican fighter Oscar Blanquet.