Ash could also develop better leadership skills. As an assistant, he might have to lead small teams during research expeditions. He would need to make decisions quickly and fairly, considering the safety and goals of the team. This would be a big change from his usual role as a solo trainer, and it would shape him into a more well - rounded character in the fanfiction.
The fanfiction might also focus on Ash's personal growth as he works closely with Professor Oak. Maybe Oak teaches Ash more about Pokémon history and lore, which in turn helps Ash become a better trainer. For example, learning about the ancient powers of certain Pokémon could give Ash an edge in battles. Ash could then share this knowledge with his friends and other trainers.
Ash might become more conflicted. He has always been on the side of good, but with Giovanni as his father, he'd have to grapple with his family ties. He could become more secretive and brooding as he tries to figure out how to balance his own values with this newfound family connection.
Ash's character would likely become more confident. Starting with a Charizard, which is a very powerful Pokémon, would give him an edge in battles. He would also become more patient as Charizard can be difficult to train at times. For example, when Charizard refuses to listen, Ash would have to find new ways to communicate and gain its respect.
Ash would likely become more responsible. Since Dratini is a relatively rare and potentially powerful Pokémon, he'd have to take extra care. This could make him think more before acting in battles and other situations.
Ash would likely become more confident with a Rayquaza as his starter. Having such a powerful Pokémon would give him an edge in battles, and he'd grow in his leadership skills as he commands Rayquaza. He might also become more responsible, knowing that he has to take care of such a rare and strong Pokémon.
In this fanfiction, Ash's character would develop in several ways. First, he'd become more empathetic towards Pokémon that are seen as difficult or 'bad tempered' like Deino. He'd have to understand Deino's needs and fears to build a strong bond. Also, his leadership skills would improve as he'd need to lead Deino in battles and on their adventures. He might also become more resourceful, finding new ways to keep Deino happy and healthy, like searching for specific types of food that Deino likes.
Obviously, the main characters would be Professor Oak and Ash's mom. Professor Oak is known for his vast knowledge of Pokemon, and Ash's mom is important as she is Ash's mother and has supported his Pokemon journey from the start.
One possible plot could be that Professor Oak discovers a rare Pokemon that he believes Ash's mom might be interested in. He then takes it to her to show her, and they end up having a long conversation about Ash's adventures and how proud they both are of him.
Ash would likely become more open - minded. Meeting a shiny ghost pokemon at the start would expose him to a type of pokemon he might not have expected so early. This could make him less fearful of the unknown in general. For example, he would be more willing to explore spooky places or deal with pokemon that have a reputation for being difficult to handle.
He could develop more patience. Since rare pokemon are often hard to find and catch, he would need to wait for the right moment. This could also teach him to be more observant of his surroundings and the behavior of pokemon. And his bond with his existing pokemon could also strengthen as they work together to catch the rare one.