HOI2 and Victoria

[Monk]

Making Japan a Great Power in vanilla Victoria is (IMO) pretty easy. All you have to do is save RPs until the Meiji Restoration event hits and start researching/trading techs+the usual building of the whole Industry+taking some colonies (Korea, Indochina and Siam are usually good to have a good colonial empire, easily defendable and provider of expensive raw materials (Mostly Tropical Wood from Siam, while Korea has a nice combination of Coal/Iron to supplement your own Japanese supply)).

Attacking China is also an option to swipe a few Silk producing provinces, from where you can expand your RGOs to acomodate some 60 POPs working in it. Of course attacking China as Japan is better to involve either joint efforts with Russia or the UK.

The biggest problem with Japan is just not falling prey to buggy events. The event line that leads up the the Meiji is so hopelessly unwilling to work for me that I gave up on civilizing Japan, even though I really like the idea of transforming them into one of the Great Powers.