He fought former WBA minimumweight champion Akira Yaegashi in his second defense at the Ryōgoku Kokugikan on April 8, 2013. Igarashi and his team had initially planned the fight against Edgar Sosa. However, when it turned out that it would not be signed, Igarashi made a direct appeal to his promoter for the fight against Yaegashi. Igarashi mentioned that while his championship belt would be at stake, Yaegashi’s popularity and recognition also would be on the line for that fight. Igarashi has so far fought against Yaegashi four times (once in his high school days, and three times in his university years) and won every time. Their trainers, Kasai (mentioned above) and Kōji Matsumoto (for Yaegashi) are high school alumni. Both are former OPBF champions and three-time world title challengers. Igarashi lost to Yaegashi in a unanimous decision.

On July 16, 2012, Igarashi barely outpointed Sonny Boy Jaro via a split decision to win the WBC, The Ring and lineal flyweight titles in Kasukabe, Saitama. He defended his both titles against previously undefeated Nestor Daniel Narvaes via a majority decision in Sendai, Miyagi on November 3 of that year.

Igarashi defeated Mexico’s Wilbert Uicab in the WBC flyweight title eliminator via a unanimous decision at the Yoyogi National Stadium Second Gymnasium on November 6, 2011.

After turning professional in 2006, he made his professional debut with a third-round knockout on August 13 of that year. Fighting out of Teiken Boxing Gym in Tokyo under Yūichi Kasai’s instruction, Igarashi gained the Japanese flyweight interim title via a split decision on August 2, 2008. Although Igarashi lost to the regular champion Tomonobu Shimizu four months later, he captured the vacated Japanese flyweight title by a third-round knockout on February 5, 2011. He defended it once, until June of the same year.

He competed for his native country at the 2004 Summer Olympics in Athens, Greece, where he was stopped in the first round of the men’s light flyweight division (– 48 kg) by Ethiopia’s Endalkachew Kebede (21:26). Igarashi replaced Nauman Karim as a lucky loser, the Pakistani fighter dropped out “due to technical reasons”. Igarashi amassed an amateur record of 77 wins (16 KOs) 18 losses, and graduated from the Tokyo University of Agriculture.

Toshiyuki Igarashi (五十嵐 俊幸 , Igarashi Toshiyuki, born January 17, 1984 in Yurihonjō, Akita) is a Japanese boxer and a former WBC, The Ring and Lineal Flyweight World Champion.