Find your tribe in a Sea of Creativity
Danny needed a new focus after fleeing his dimension. Unfortunately due to the lack of ecto in this dimension it couldn't be just any place, he had to find an unclaimed temple or alter of sorts that was still receiving offerings he could convert into ectoplasm.
He found it in the form of an alter in a mansion's attic where the scrawniest child he has ever seen spent enough time exploring his own parents finds to uncover an abandoned alter in which he has built a routine of leaving offerings to near daily.
At first he only visited to collect power from the offerings, spending the rest of his time exploring the city he now knows as Gotham. But as he hears more and more of the kids prayers, he can't help but get attached enough to watch over him. It's not like his parents are watching over him he soon finds!
TLDR Tim finds a dusty alter in his attic and leaves stuff on it as offerings while he speaks about his day and his plans for the night, Danny finds the alter has no entity attached to it and claims it as his own soon getting attached to Tim