I suppose your title would have been enough to give great answers --- but your OP leaves me in complete perplexity to understand your common reasoning that when combined with your misinformation and your ability to autoresponder to your conjecture in that same OP and then you walk away of that analysis to fall into a new question that is pregnant with the first, two different births, yes, two questions, the title and the closing of the OP.
You ask yourself, you analyze and you answer yourself, but even if you come to a conclusion (according to your analysis) with bitcoin, which should be decisive, ou come back and ask the same thing. Oh, no! bis...
Since i joined bitcointalk forum i find it difficult to make a post relating to bitcoin, bitcoin is like physical money (fiat)...//,,,
No.
...//,,, and i want to know the difference between fiat and bitcoin, and without fiat existence can bitcoin have a name?, after thinking all this with seriousness i concluded that bitcoin and fiat works like brothers and sisters and no one can leave each other....//,,,
No, they are not related even if your reasoning wants to do it, that's why you get confused.
...//... so i want to know if any other digital currency can function without fiat?.
ooh!! Yes, bitcoin on the Bitcoin network.