There is zero possibility of Japan fully reflecting on its past and cooperating with Korea

People compare them to Germany, but Germany has never apologized to Africa either.
The reason Germany apologized is because the counterpart was a victorious nation and they were interconnected within the European continent.
Even the victorious United States doesn't tell Japan to reflect on its past, so even if Korea tries to mumble about historical issues, Japan won't give them the time of day.
Furthermore, Korea is a small nation, and rather than being a merit to Japan, it is a competitor located across the sea.
Most decisively, the descendants of war criminals are currently dominating the Japanese political scene.
The US covered up for Japanese war criminals to prevent the spread of communism, and they erased their history to hide their flaws.
The Japanese people currently calling for friendly Korea-Japan relations are not the mainstream.
Since political succession is possible in Japan, settling the historical issues between Korea and Japan will remain impossible in the future.
The best they can do is maintain a relationship of "too close to be friends, too far to be enemies" through trilateral cooperation between Korea, the US, and Japan.