New answers tagged naming
If you are quoting the girl, or writing from her perspective, than you should have her say what she would say if this was real life. The fact that a statement isn't true (in whatever sense) doesn't mean a character in the story shouldn't say it if that is what the character would say in real life. To take an extreme example, if I was writing a story in which ...
If the story is told from the perspective of the girl, either in first or third person, she will think of him as her father and that is what you must call him, anything else will feel contrived. Only if you are not writing from the perspective of the girl, but from an omniscient or neutral standpoint, can and should you use terms that she would not use ...
So, this is a third person narrative, and character X knows that Y is not her real father, but the reader doesn't? I would go with language that matches what the reader knows --i.e., refer to him as "X's father" until you're ready for the reveal. If it's true third person, you could just call him by his first name, but I can understand if you want to ...
I would use synomymouses for father, for excemple dad, daddy or father. If you use more languages in your story you can also use the words for father from both languages, language A for one and language B for the other.
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