Korea was being brutalized by the chinese, russians and even their own nobles. Japan couldn't just stand by watching their neighbours suffer and had to save the Koreans from this great injustice. Even though Korea had been aggressive and belligerent towards Japan in the past, the noble Japanese forgave them and intervened. Hence the historically correct term Humanitarian Intervention of 1910. Under the selfless tutelage of the Japanese, Korea entered the modern era.
Well let's not forget how they also liberated Taiwan from stupefying Confucian ways, and started them on the road to becoming a land of industry and rational inquiry. It was an awesome burden the Japanese bore, but they took it on gladly.
To this day, the places that Japan wisely led are far more developed than their neighbors. How about that?