>>52027475With Dawn? Yes. They were shilled extremely hard as a duo and Brock is often considered an awkward third wheel to them. Dawn is also the companion with the most appearances (DP, BW, referenced in XY, appears several times in JN) and is the only one who went through the effort to watch Ash battle Leon live to cheer for him.
Serena honestly didn't have any chemistry with Ash to my recollection. A lot of it was her one-sided interest in him. Ash obviously cared about her as a friend but they come across as the weakest out of all of Ash's previous relationships with female companions like Misty, May, Dawn, Iris (Yes really) and The Alola girls. She meshes with him more than maybe Koharu who genuinely has never given a fuck about his existence.
Despite that lack of chemistry, Ash/Serena was honestly the most pushed ship by the actual show but that all revolves around her crush on him and nothing more. Amusingly, Ash even ghosts her when she sees him for the first time in JN and had to be stopped before he recognised her. Meanwhile he instantly detected Lillie's presence when she was behind a wall and saved her life.
