That's my family name. Hifumi is my given name. [She should probably just... stop using her family name in introductions, because this is at least the second time it's confused someone, but old habits die hard.]

Well, that at least means there's more than two of us from Japan here. It's a marker of both respect and relative emotional distance - we rarely just use someone's given name to refer to them. There are a few other honorifics that mark closeness of relationship or the relative ages of the people involved, but 'san' is the most common one.