While my travel story is under way, an advice should you ever come to visit your colleagues in Japan.
Whether it is holiday or a business trip, as a rule, everyone brings something. And something in this case means some sweets or snacks from the place you are coming from. While something similar may exist in France, but it would be more an exception than a rule.
Now imagine what happens in the office after the longer national holidays, e.g. Golden week in spring, Obon in August and etc. Traveling within the country also counts as a trip, so you can get familiar with regional sweets and snacks even before you go there!
Forget the diet, it is mid-September and I still have some reserves in my desk drawer.
If you happen to be coming over from France, have in mind that most likely they know what is Ladurée and that Ladurée macaroons are the best and the most expensive. No obligation, but will surely make an impression to your colleagues. Just a hint!