It has been long since Japanese traditional Breakfast became western style.
The bread is square white bread.
Croissant is not popular at all, we can call square white bread as our national bread.　Most of the bread in the supermarket and convenience store is made with egg, but only white bread is made without egg(nor milk).
Usually white bread is vegan.
Still,-I don’t know the situation in other countries- but sadly Japanese white bread from the big factories contains a lot of sugar, salt and food additives.
I think we better buy bread from local baker who doesn’t use unfamiliar additives.