From the Portugese "pão." Although bread was initially also called "mugi-mochi," "mushi-mochi" or "mugi-men," "pan" has become the normal name.
In the last decades of the 16th century bread was brought to Japan by Portuguese missionaries. It was however not eaten by the Japanese, perhaps because the taste did not suit them, or because of its strong association with Christianity which was forbidden in Japan from the early 17th century. The Dutch in Nagasaki had bread baked locally, but again only for their own consumption, and the bread they gave as a present to the shogun when visiting Edo was seen as not more than a curiosity. One Edo-period cookbook contains a recipe for bread, but that turns out to be for Chinese-type mantou rather than European bread. In another book with recipes from 1718 there is mention of using yeast for making bread, but as the yeast appears to be amazake it is questionable whether that recipe worked at all or whether it was ever used.
Egawa Hidetatsu ("Tarozaemon"; 1801-1855), an official from Nirayama in Izu who also studied Western-style artillery and built the Odaiba fortifications in Tokyo Bay, was reputedly the first Japanese to bake European-style bread. But that was a special type of hard bread and it took until the Meiji period until bread became a little bit better known in Japan, due to two reasons: (1) the invention of anpan by Kimura Yasubei in 1875 and (2) the proposal by German army doctor Theodor Hoffmann to introduce bread as food for the army to fight beriberi in 1890.
The invention of Anpan was the most important event, as this became the template for all Japanese-style bread. After all, the Japanese already had rice as staple food and they liked rice better than the sour bread. Rice also fitted their whole food culture. So bread only could fit in as an extra, a snack. And this has basically continued until today, although in the last decades people also do eat toast for breakfast, or sandwiches for lunch. But that is an option, not a custom.
Most bread you find in Japanese bakeries and supermarkets strictly belongs in the category of "sweet bread" or "savory bread." In other words, most bread in Japan is a snack like confectionery. (Of course, there are exist good European-style bakeries making wholesome types of bread, but these are rare and limited to the big cities or some department stores).
So bread as a snack in Japan has followed its own course and flowered in unexpected ways. Here is a list Japanese snack breads, divided into "sweet" and "savory":
Written with information from the Japanese Wikipedia article on bread.