>>34203910Ash's current hat is in USUM as a customization option called the "Hero Cap", and he's referenced in the Pokedex entries for Cap Pikachu
>Ultra Sun: This form of Pikachu is somewhat rare. It wears the hat of its Trainer, who is also its partner.>Ultra Moon: This Pikachu is wearing its Trainer’s cap. Since the cap’s not the right size, the fit is a bit loose. 