I just notice this trend in the Danny Phantom x Batman fanfics... is how y'all widen the gap on the Fenton Family. More specific, between the parents and Danny.
In most fics, Danny ran away from Amity Park. And there are 2 sub category of why he ran away...
First and the most common, is that his parents, Jack and Maddie Fenton, find out that Phantom is Danny and reacts negatively. This happens when they walk into a place while Danny is in the middle of transformation. Now the reactions on the discovery differs: whether Danny immediately bails and fled, or is captured experimented on and his friends and his sister are the one who bail him out. And in some, the parents just gave him to the GIW! The thing is, his parents have strong dissociation on Danny and Phantom, to a point they thought that Phantom killed their son and is posing as him.
Second and... what Danny is most scared of... is his parents, his sister and his friends died. The plot depends though, there are some fics only his family died but his friends are still alive and in some his sister is alive. Also depends on the timing and who done it, like if this is TUE where Clockwork did not save his loved ones, then Danny ran away to avoid Vlad and prevent his future self. In some, GIW did the deed because the parents (who discovered Danny is Phantom but they still love him) refused to give the ghost boy to them.
Like give the boy trauma, whether his parents experiments on him or kill them, then ship him off to Gotham so Bruce can adopt him...
And the last one on the list... is pretty much the tame and does not involved experiments, death of the family and friends, and Bruce's adoption problem.
Is that Danny distanced himself, sometimes along with his sister, after graduating high school and moving to a new place for college/university.
In this plot, Danny is able to keep his ghost half a secret and went thru his life as... well... intact as possible. However, something happened to the family dynamic of the Fentons, and both Danny and Jazz ended up distancing from their parents.
That's pretty much it... the most used plots that involves Danny leaving Amity Park, whether he is traumatize or not 🙂