He made his first defense later that year, knocking out the challenger only 24 seconds into the first round to set the record for the shortest Japanese flyweight title match ever.

Naito challenged Wonjongkam for the second time on October 10, 2005, but lost by decision after the fight was stopped due to an injury in the 7th round.

[4] The fight received widespread coverage by the Japanese media because of the heated exchanges between Naito and the Kameda boxing family.

Daiki Kameda had described Naito as a "cockroach" prior to the fight, and stated that he would commit harakiri (ritual suicide) if he were to lose.

[3][5] The victory gave Naito celebrity status in Japan, and he has appeared in numerous Japanese television programs and commercials since then.

This bout was on the same card as WBA flyweight champion Takefumi Sakata's 4th title defense, and Koki Kameda made a surprise appearance on the ring to congratulate Naito during the post-fight interview.

On November 29, 2009, he lost the WBC lineal flyweight titles to Koki Kameda in Saitama, Japan, losing by unanimous decision.