Both have been heavily traumatized in the past. Both suffered greatly because of their older siblings- Aeron had Balon and Euron, by whom he was despised and possibly molested, and Arya had Sansa, who told Cersei of Ned's plans (leading to their fathers' death), and constantly called her Horseface in front of her fathers' men.
Moreover, both know how it is to be taken prisoner and losing siblings, which adds to their similiar backstories. It will surely be a relief for both of them to know there is a person out there who truly understands what they had to go through in their lonesome lives. They both turned (so far) to impersonal people, in contrast to the sociable people they once were, and may be again, with each others' help.
As we all know that relationsships rely heavily on similiar activities and interests, and both sought refuge in a god and kill for this gods' sake, believing it gives them power; Aeron kills for the Drowned God, Arya for the Many- Faced- God, or death. Since both gods are likely faces of the Great Other, their believes would match even better.
And finally, they have very similar names- Aeron and Arya. Aerya sounds awesome.
What do you think?
Edited by John Doe, 29 August 2014 - 02:10 AM.