^Well yeah. We're just talking about their similarities. Like how Hylia might have created Fi as a good version of Ghirahim. Like I said before, Ghirahim is Dark Fi.
I don't think they are the same because ghirahim stayed until links time but so did fi even if the godess turned ghirahim into fi when demise died didn't they both get sucked into the Master sword? but fi also stayed in the master sword... so maybe ghirahim was reborn as fi like you said but he's a spirit of a sword could he be reborn?
They probably are counter parts Link Demise and Fi and Ghiriham, the Master Sword has a blue crystal like Fi's chest, Demise's sword has a red one such as Ghiriham's waist.