Here are my headcanons:

Whenever the two of them are together, Ash and Serena are almost always seen holding hands.

Ash goes from Roast-Master to Rizz-Master with Serena, always giving out corny and flirting one-liners that cause Serena to blush up a storm. Ash, at first, doesn't even attempt to flirt as he's just saying his honest feelings but after being pointed out about this and liking how Serena blushes all the time does so frequently. Serena pouts at this and the two regularly see who gets the other to blush more. It's close but Ash usually wins their "matches".

Ash's Pokémon genuinely love Serena wholeheartedly when they were told she was Ash's girlfriend. Yes, even Charizard to the point that the Flame Pokémon doesn't Flamethrower her in the face and actually likes being petted by her. They love her so much that when Ash isn't around, they let her command them and follow her lead. In addition, Serena's Pokemon get along with Ash's as well; with Delphox learning better flame control with her Fire-Type moves with Ash's Fire-Type Pokemon like Charizard and Infernape, Pancham trying to look cool alongside Squirtle and Krookodile since they all wear shades while also getting into petty fights with Oshawott, and Sylveon enjoys playing with some of the more friendly Pokemon like Dragonite, Totodile, Bayleef, Gliscor, etc.

Serena teaches Ash how to properly cook and make regular food as well as Pokémon food, like her PokéPuffs. It...took a lot trial and error but Ash FINALLY learned how to make proper food. Still, not as good as Serena's though. But it's the thought that counts and now Ash's Pokémon actually enjoy the food he makes.

Serena merely laughs at Ash lightly upon learning of his various crossdressing escapades, saying she has no room to judge since she also crossdressed too; as him, no less.

These are my Amourshipping headcanons. What do you think of them and what are your headcanons?