South Korean President Park Geun-hye, who refuses to hold a summit with Prime Minister Shinzo Abe, met Monday with visiting opposition leader Katsuya Okada.
Okada, head of the Democratic Party of Japan, has said he wants to supplement the government's efforts in diplomacy with South Korea.
He also met with Foreign Minister Yun Byung-se in the afternoon.
"The relationship between Japan and South Korea is not at its best and public sentiment of both nations remains harsh," Okada told Yun during their meeting. "Although I am in the opposition bloc, I hope to improve the relationship as best as I can."
Before heading to South Korea on Tuesday for a three-day visit, Okada said last week: "This year marks the 50th anniversary of Japan's normalization of relations with South Korea and the 70th anniversary of the end of World War II, yet bilateral relations are regrettably not in good condition."
Okada was invited to visit South Korea by Yun when the two met on June 22 while Yun was in Japan.
The Abe government is currently trying to set up a summit with Park in September.
It would be the first Japan-South Korea summit since Park came to power in 2013. She has declined to hold a summit with Abe over the "comfort women" issue, in which females were procured from the Korean Peninsula and elsewhere to work at brothels for wartime Japanese servicemen.
Diplomatic relations between Japan and South Korea have been strained over other history-related disputes, as well as the Takeshima/Dokdo territorial dispute.