He became a fan of WBC Bantamweight champion Joichiro Tatsuyoshi, and entered his school's track team to build up his stamina.

Nashiro won by 10 round unanimous decision, becoming a world ranker in only his 5th professional fight, and was hailed by boxing fans as one of the top prospects in Japan.

Nashiro defended his title in November 2005, winning by 10-round decision, and became the top ranked contender in the WBA Super flyweight division.

[1] Garcia had previously been invited to Japan as Nashiro's sparring partner when he was training for his fight against Martín Castillo.

Nashiro fought former WBA super flyweight champion Alexander Muñoz on May 3, 2007, at the Ariake Coliseum in Tokyo, Japan, for his second defense.

On September 15, 2008, Nashiro regained the WBA super flyweight title by the split decision victory over fellow Japanese Kohei Kono.

Prior to this bout, the title became vacant because Munoz lost it to WBC champion Cristian Mijares who unified it.