In my wanderings around Japan giving my kana knowledge some practice I've noticed both the words "ガール" (gāru) and "ガールズ" (gāruzu) in use at least in signage. Obviously they are borrowed from English "girl" and "girls" in turn, but is either or both of them now considered to be Japanese words, or are they merely seen as English written in katakana?
If they are now considered to be Japanese words, how do their usages differ from the native Japanese words for "girl"?
And if both are now considered Japanese can "ガールズ" be considered a plural of "ガール", especially since Japanese doesn't normally have a grammatical concept of plurality?