I actually run a Japanese business (franchise) in the US so I go there for business a lot. I'm guessing you will have someone with you who will be acting as more of a liaison/translator, so you probably don't need to worry too much.
There are a lot of little politeness tips specific to business that I could give you, but the most important thing I've learned is that a lot of Japanese business is done the old fashioned way, with a verbal contract over drinks. Deals between companies are done based on trust. So just be careful what you say/agree to in these situations, no matter how drunk everyone is. You will be held to it later.
Also while it can seem kind of harrowing the first couple times this happens, don't be too afraid or uncomfortable if your Japanese colleagues start asking really gossipy questions really early about your business, especially if you go out socially with them. I think it's part of the way they build trust, and there seems to be kind of an unwritten rule that the things you say in situations like that are in strict confidence. Obviously don't give anything away that's really confidential, but they're probably going to tell you things themselves that you wouldn't expect to hear, so you gotta throw them a bone once in a while. That seems to be how they know you're in this thing together.
Business in Japan is fun and interesting like most of the rest of the country. It's very different to business in the US.