Originally Posted by
hailstorm
You're a foreigner, so you will not be required to conform to Japanese rules.
You don't need to get into the details...just tell them in advance that you cannot (not will not) drink alcohol, refuse when you need to, and that will be that.
I totally agree with Hailstorm. Don't overly concern yourself.
On the other hand, the OP wants to make the situation as smooth as reasonable (which is a Japanese way of thinking), so I think that in this case of a formed relationship it's OK to do some ground work ahead of time.
Edit to note: Actually, reading the message again, maybe I just repeated haistorm's advice!