Ah, that is more clear and helpful. Context is everything when it comes to deciding what words best convey your scenario and thinking...
On that note:
"If you work for a company in Japan and go on vacation, it is customary to buy souvenirs for your co-workers.
Note: I personally would use gifts in place of souvenirs.
You can also replace customary to "ideal" (if it's not a true custom).
My personal version: When you work in Japan, it is ideal to buy gifts for your coworkers on your vacation.