SORRY FOR LATE ANSWER

trevor: has a Kalosian accent. unusually wealthy but it’s at the cost of his parents being absent and sending child support to him and his sister. Seems naturally or effortlessly smart but he actually studies a lot.

Serena: originally from Unova. In a similar vein to Trevor, her “natural” skill at battling comes from a lot of failures and hard work endured in Unova.

As a couple, part of the reason they’re so fond of the other is when they learn what they think comes so effortlessly for the other is actually built on hard work. And that just makes them admire the other more!