From an interview with XYZ's director that confirms Serena kissed Ash.

Notes:

Translation from Adamant: Interviewer: "I didn’t watch the final episode, so this might be a dumb question, but what happened to Serena’s love, did she and Satoshi become a couple in the end?"
Tetsuo Yajima: "They didn’t become a couple in the episode itself, but the way I ended it is meant to make you understand that they’re probably going to become one later. Serena tells Satoshi that she’s going to improve herself and then come back to him. And then she does something absolutely incredible when she leaves (laughs). She’s meant to be kissing him in that scene, but since I couldn’t just have them kissing on screen, I had Serena’s feet “float” upwards instead."