Serena represented a classic romantic crush for a single generation (XYZ), which fit perfectly with Kalos being inspired by France, the land of romance, fashion, and elegance. That was her specific role for that season. But once the XY era ended, so did that storyline. Misty, on the other hand, is the only PokéGirl who has consistently made cameos and retained a unique status throughout the entire series. Regions come and go, but Misty has always held a special place right in Kanto and in Ash's home alongside Delia, as the companion who waits for him to return after a long journey. No other PokéGirl was ever given that kind of role. While others were introduced for regional marketing, Misty remained the constant back home.