South Korea has worked hard to improve relations with Japan so far, but changes to the policy line are unavoidable after Japanese Prime Minister Shinzo Abe paid a much denounced visit to a controversial war shrine, a ranking government official said Friday. The remark means Seoul takes Abe's visit to Yasukuni Shrine very gravely and suggests the country could become more assertive in demanding Tokyo atone for the sexual enslavement of Korean women for its troops and other atrocities committed during its 1910-45 colonial rule of Korea.