Tsukasa Yoshida won the women's 57-kg division at the judo world championships on Saturday, while compatriot Soichi Hashimoto settled for silver in the men's 73-kg class.
Yoshida's gold made it four for Japan from six divisions for men and women combined after three days of action at the National Gymnastics Arena in Baku, Azerbaijan.
In the women's 57-kg final, world No. 2 Yoshida had an ippon victory over last year's bronze medalist and world No. 5 Nekoda Smythe-Davis of Britain.
The 22-year-old Yoshida claimed her first world championship title after settling for runnerup in her debut tournament last year.
"There is a huge difference between winning gold and silver. I'm really happy, but I'm relieved," Yoshida said.
"I knew I was stronger than (Smythe-Davis)," she said. "The win is a huge confidence boost ahead of the (Tokyo Olympics)."
She advanced to the final by beating Canada's Christa Deguchi, who was born and raised in Japan but decided to represent her father's home country to increase her chances of competing at the 2020 Summer Games.
Deguchi took bronze along with defending champion and world No. 1 Sumiya Dorjsuren of Mongolia.
Hashimoto failed to defend his title in the men's 73-kg class, losing to South Korea's An Chang-rim by ippon in the final. Iran's Mohammad Mohammadi and Azerbaijan's Hidayat Heydarov claimed bronze.
Kosei Inoue, Japan men's judo head coach, said Hashimoto had trouble with his right eye after hitting his head during his semifinal bout earlier in the day.
"I didn't have any vision in my right eye (during the final). But a loss is a loss," Hashimoto said.
"I'm going to start over from scratch so I can make use of this (defeat)."
Some 750 judoka from 125 nations are scheduled to compete at the weeklong tournament.