Of course, I'd imagine Japan's route wouldn't take a 180 from their historical route. Still, Japan would probably attempt to Japenseise(Is this even a word) it's colonies. I'm sure Japan's government would understand that being at least somewhat benevolent to it's colonies helps in the end.

Or they could do what the Italians did to Libya. Build tons of schools and roads, and send tons of Italians to live there in an attempt to fully integrate it and care no shits about the natives. Though... there are a shit ton more natives in Korea then in Libya.