Because of the fear and chaos that Vikings and dragons stir in both each other and to civilizations beyond, Pitch would naturally turn to Berk at some point in his immortal life.
Hiccup in particular would feel a great sense of fear and despair that would make him stand out to Pitch, picking at the boy's feelings of inadequacy and self-loathing, as well as the fear he would feel from bullies and raiding dragons to keep himself well-fed. With that said, the two would understand each other on a level the other vikings on Berk would not. Both yearn for friends - possibly love - and live in a realm they are outed by.
Should the story happen during or after the events of How to Train Your Dragon, Toothless would naturally be overprotective of his rider, Hiccup ignoring the dragon's behavior to help mend the poor Boogeyman's melancholy.