This is a video game exclusive trope, where a certain character is only heard in recordings you find or read about in letters. They can go through whole character arcs, and it's this that makes them not the Ghost or the Voice; if all artifacts related to them were viewed chronologically, it'd basically be a story within a story. This certainly needs a better description and name but I think it deserves a page.
Hello, Unknown Troper. You'll need to get known to lend a hand here.