Japan offered an apology and a USD 8.3 million payment Monday to the 46 surviving South Korean women, under an agreement which both nations described as "final and irreversible."
The plight of so-called "comfort women" forced into World War II army brothels is a hugely emotional issue that has for decades marred ties with Japan, which ruled the Korean peninsula from 1910 to 1945.
The landmark deal has met with an angry reaction from victims and activists, who took issue with Tokyo's refusal to accept formal legal responsibility.
"The fight is still on," survivor Lee Yong-Soo said at the protest in front of the Japanese embassy in Seoul, attended by one other victim and about 250 protesters.
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Gatherings have been held weekly there for years, demanding Japan's formal apology and compensation.
"We will continue to fight to make Japan take formal, legal responsibility and apology so that victims who have already perished will have justice," 88-year-old Lee added.
The rally was sombre as the lives of nine former sex slaves who died this year were commemorated, but later turned angry with protesters shouting slogans denouncing Japan and its prime minister Shinzo Abe.
Some chanted slogans of "Cancel the humiliating agreement!" and waved banners that read: "Say no to relocation of the statue!".
South Korea's government must now win public support for the deal, which has had a mixed reception with the media also taking issue with the terms.
The handful of comfort women who have spoken about the agreement have mostly rejected it, but the views of the others are not known.
Up to 200,000 women in Asia, many of them Koreans, are estimated to have been systematically forced to provide sex to Japanese soldiers during World War II.