When Ash catches Greninja, it might change the dynamics within his team. Greninja could be a bit of a loner at first, not really fitting in with the rest of the Pokémon. But over time, through shared battles and experiences, it could learn to work well with the others and even inspire them to improve.
Well, one possibility could be that Ash has been on a long journey to find and catch Greninja. Maybe Greninja is a super rare and powerful Pokémon that only appears in a very specific and dangerous area. Ash, being the determined trainer he is, overcomes many obstacles like battling other tough Pokémon and traversing difficult terrains. In the end, he uses his skills and the bond with his existing Pokémon to catch Greninja.
Well, in Alola, the battle environment is different. Ash Greninja has to adapt to the new battle rules like Z - Moves. It may start by observing local battles and learning from them. It could also adapt to the more friendly and less intense battle atmosphere compared to other regions. This means it might have to change its battle strategy a bit, not always going all - out from the start. And it might interact with different types of Pokemon that are native to Alola, which could lead to new friendships or rivalries, further shaping its adaptation to the Alola environment.
Well, for one, Haunter has some really cool moves like Hypnosis and Dream Eater. When Ash catches it, his team's battle strategies would change. His other Pokémon would need to learn to work with Haunter. Also, Haunter's presence might intimidate some of the opposing Pokémon, giving Ash an edge in battles. It could also open up new exploration opportunities as Haunter might be able to access areas that other Pokémon on his team can't due to its Ghost - type nature.
There could be unfinished business between them. They might have a shared goal that they haven't achieved yet. Greninja's return to Ash in the fanfiction could be to finally complete that goal, whether it's winning a particular Pokemon tournament or saving a certain place from destruction.
His other Pokémon like Rowlet might be in awe. Rowlet is a curious Pokémon, and having a mythical Pokémon like Tapu Koko around would be fascinating. It could learn a lot from Tapu Koko, especially in terms of using its unique powers more effectively. The whole team would likely feel a sense of pride that Ash was able to catch such a rare and powerful Pokémon.
If Ash catches Meowth in the fanfiction, it would be a huge blow to Team Rocket. Meowth is the translator for their Pokémon, so without it, they would have a hard time communicating their plans to their Pokémon. This could lead to a lot of failed missions.
His confidence could grow in a different way. Usually, Ash is confident in battles, but this time, when he catches these rare Pokémon, he might gain confidence in his ability to understand and bond with Pokémon that are very different from the ones he's used to. He could start to see himself as a more well - rounded Pokémon trainer, not just one who battles but also one who can form deep connections with all kinds of Pokémon.
At first, Ash and Eevee might be a bit cautious around each other. Ash is excited to have caught a new Pokémon, but Eevee is in a new and strange environment. As they start training together, they build trust. Eevee might learn new moves from Ash's guidance, and Ash learns more about Eevee's unique abilities.
Greninja might adapt quickly. It could use its natural agility to explore the new terrains of Alola. The warm climate and different types of water sources might be new to it, but it could adjust well. For example, it might find new hiding spots in the Alola forests or enjoy swimming in the crystal - clear Alola waters.
They might perform amazingly. With Pikachu's speed and electric attacks, they could easily take on many foes. Bulbasaur's grass - type moves could provide good support. Maybe they'll win most of their battles and gain a great reputation in the fanfiction world.