Guys. What if, hear me out, Danny is that rumored (never aging) spooky ghost story people tell each other. (Only its somewhat real, cause Danny is half ghost and is aging slowly) Like imagine Danny 'works' at the library in Gotham, he meets like Jason as a kid, helps him find a book and when Jason goes to thank him Danny is just gone. Then Dick comes to picks him up, asks how the library was, he explains only for Dick to look pale and staring at Jason a little freaked out cause Jason just described the guy he meet as a kid himself years ago, same name too, then when Bruce comes home, he too tells a story of running into Danny at the library. When he was a kid too.
Then it happens with Tim, Cass, Steph, Duke, even Damian later in the following years.
Basicly Danny is the rumored ghost story at the library. (He only 'works' there cause Ghostwriter library is connected to it via portal door that opens randomly and Danny is only there on certain times/days to make sure no one uses it and steers people away from it by helping and getting them out of the area. He's helping GW out as an apology for what started their Christmas fight, and if Gw lets him look at some rare space books/tomes than yeah, might as well)