Japanese companies often hold parties among the members of staff. Typical ones include welcome parties for new employees, farewell parties on the occasion of personnel changes, and year-end parties to express thanks for all the work and support during the past year.
It’s also common for colleagues to have dinner together while drinking alcohol or tea after work. If you cannot drink alcohol, there’s no problem with refusing, but you’re advised to use polite words. The ideal way of refusing is to include the reason and say Sumimasen, o-sake wa nomenai n desu, meaning "I’m sorry, but I can’t drink alchool."
Parties are a good chance to get familiar with everyone and even discover unexpected sides of your colleagues, so please attend them if you are invited.
