Little prince! Au where Ash’s father is the only king left standing in Kanto, and one of the few remaining kingdoms like Rota and the Azoth kingdom in the world.
Ash is the prince and heir to the throne of Ikklas’a Kingdom but unlike the other princesses and princes Ash is treated much differently. His mom and dad split up when he was just three weeks old bevause Delia couldn’t deal with the stress of being queen on top of taking care of a baby, she also didn’t like the thought of nurses and ladies in waiting taking care of her son at all, so she approached her husband with the attention of an easy divorce.
Aaron was kind and gentle because he still loves Delia and though it would put a strain on their relationship as a whole and their new born son he agreed to the divorce. They settled with Delia raising Ash for most of the year and the summer months Aaron got parental rights over Ash. This allows Ash to experience a normal life and also one of a Prince for short stints of time. This also doesn’t stop Aaron for singing Ash up for tutors though much to Ash’s charging when he gets older. Aaron is his father and even though he would burn Pallet Town to the ground he would much rather not start another century long war his great-great-great-grandfather finished. 
Ash grows up knowing not to mention that he’s a prince, much to his hate especially when Gary starts to bully him, to other people outside of Ikklas’a and to only do so in very dire emergency. Only a few people outside of the kingdom know such as Delia and Lance along with his elite four in Kanto.
King Aaron is kind of his own “champion” for his people in a sense. They play mostly by Lance’s rules and make sure not to step on to many toes but this also means that no laws shall pass unless Aaron looks them over for himself. It’s a give and take kind of relationship between the two governments.
Like Rota and Azoth any trainer or other kinds of people like visitors and merchants are allowed and warmly welcomed in the kingdom. They hold contests and lots of festively because the king and the court love their rich history in story telling, foods, and crafts. Even though their actual history is filled with many wars. Aaron wants to make sure that all people in his kingdom feels safe and loved and that people that are being mistreated and swindled stay down to an extremely low number as much as Aaron can make it.
Like normal kingdom stuff there’s trade routes and kingdom meetings that are held with the other queens and kings of the world. Sometimes a few champions or other league delegates come and join them from their respective regions to make sure that their give and take relationship stays the same across the board and thet their not being to oppressive and that the kingdoms won’t start another war. This means that Ash sometimes, though rarely, gets brought to these gatherings with his dad. He is the future king after all and if Ash doesn’t want to be king it’s still a nice thing to learn.
Ash has met Rota’s Queen Ilene and some other princes and princesses like princesses Kimia. She was nice even though she liked scaring Ash and pulling on his hair because it was apparently “super-super-extremely-out-of-this-world soft” which made Ash hide because his papa’s legs.
As Ash grows up and Aaron’s love ten folds every second for him that doesn’t stop from Aaron wanting Ash to experience his own life. So he has a deep conversation with Ash about how he wants his son to go on as many adventures that he wants and to experience the world as a whole and every wonderful, and not so wonderful, thing about it. Aaron never had his own chance to go and have his own journey when he was a kid since his own father was much more strict so he’ll live through Ash but by bit with every letter he sends back home to the castle explaining his journey.
Aaron just wants expecting his sweet Érzi to send an actual, and verified by his advisor and head general, Ho Oh feather in Ash’s first letter and then get explained a year later that his son is Arceus’s Chosen One.