The interesting thing about Japanese is that, unlike most other languages, it writes loanwords differently than native words: they're written in the katakana ch

The interesting thing about Japanese is that, unlike most other languages, it writes loanwords differently than native words: they're written in the katakana character set rather than kanji (Chinese characters) or hiragana. So "pan" is one of these, since it was borrowed from Portuguese. This rule isn't absolute, though: coffee has a (rarely-used) kanji version, and tobacco ("tabako") is written in hiragana, as is tempura. Sometimes if the word is old enough, it gets treated as a native word.