If there is a character in a series who hasn't been given a first name, how do you handle that in fanfic? If, for example you are writing him in a scene where there is a need for someone to use his other name, what do you do? Write around it somehow, which can lead to the story sounding unnatural? Or just use the surname, which may have the same problem? Or is it acceptable to give the character a name? Personally, I don't like that idea, mostly because it doesn't seem right to name somebody else's creation, but also becuase if at some point he gets given a name, your story is going to sound odd.
Maybe the easiest thing to do is not to write it.
If anyone is wondering, I'm talking about Sergeant Wu from Grimm, and I'm not actually writing anything yet, it's just a theoretical question at the moment.