If you could wank Japan into an empire 2-4 hudred years before they had one otl, I can imagine a world where the British and Japanese divide up the world. It would take a cocky Britain that never makes any friends in Europe, and who majorly distrust the US, maybe for losing Canada. The British identify with this new island based empire, while assuming they could conquer it if necassary, while the Japanese assume the same. However with so many potential gains, the two utilize the friendship to try to push all others out of colonialization. In this tl I'd imagine the British developing a nazi-ish identity as a master race, with the Japanese being looked at the same as otl Nazis did. Oh, and they would definelty turn on each other eventually, but point is I could imagine Japan getting a little of Africa so no other European does in such a scenario.
But how to get Japan there without going asb? I don't know enough to say it's possible, especially without butterflying quite a bit, though with a pod in the 1600s in Japan, European colonialism may go roughly the same for a while, so there's a decent portion of time to work with at least.