The 24-year-old judoka defeated Dayaris Mestre Alvarez of Cuba, the 2006 Central American/Caribbean Games gold medallist, by an ippon four minutes one second into the final to retain the women's 48-kilogramme title.
The finals of three classes were all-Japanese affairs, with young hopefuls Naohisa Takato winning the men's 60kg, Yuki Hashimoto winning the women's 52kg and Anzu Yamamoto winning the women's 57kg finals.
Takato defeated Hironori Ishikawa by an ippon, while Hashimoto eliminated defending champion Takumi Miyakawa in the semi-finals and went on to beat Nodoka Tanimoto in the final.
Yamamoto defeated Nozomi Hirai to wind up the day's events, shortly after Jumpei Morishita defeated the last foreign contender, David Larose of France, by an ippon in the men's 66kg event.