The japs wouldnt be a good addition to the coh2 for several reasons: they were completly different from the four other factions (few combined arms, heavy usage of ambush taktiks, suicide attack, etc). The military focus was more on navy battles than on big armoured vehicle assaults(although I want to see the yamato cruisin around in the volga

). They were experts in jungle skirmisches, camoflaging in bushes or surprise attacks, but they would lack in tanks for european battlefields. I can imagine them being an excellent and fun-to-play-faction that I'd actually love to see in action but they dont fit into coh2.maybe in a fourth coh or a seperate multiplayer.
I dont think jap is racist. Some people might think its racist because its a bit sloppy probably overused. Its like "jude"(jew) in germany, many people think its racist but it actually depends on the context, could be said in a humiliating way or in a friendly/funny/normal/shortend/whatever way, the situation makes it racist.
