Unification will give Korea an advantage in entering the continent.
Japan’s inability to jab in terms of defense resources, etc.
Japan will try to provoke North Korea to share control over the North on its back in the event of a war.
It’s similar to the Japanese Invasion of Korea in 1592, when they targeted Korea under the pretext of entering the Ming Dynasty.
If the relationship between the U.S. and Japan becomes closer to passing Korea as it is now, pro-Japanese to Japan will become crazier.
So maintaining the Cold War is the pro-Japanese strategy, similar to right after liberation.