A really interesting plot twist could be that the Eevee is not what it seems at all. It could be a transformed Pokémon, like a Ditto that has taken on the form of an Eevee for some reason. This would completely change the dynamic of the story and Ash's relationship with it. Also, the Eevee might be the target of a group of villains who want to use it for their evil plans, and Ash has to protect it from them.
One common plot twist could be that the Eevee turns out to be a shiny. In many fanfictions, this adds an element of surprise and rarity. Another could be that the Eevee has some sort of special ability that Ash discovers later, like being able to communicate telepathically. It might also be a plot twist if the Eevee is actually a key to unlocking a hidden power within Ash himself.
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.
One popular 'Ash Catches Eevee' fanfiction might be the one where Ash catches an Eevee in a unique forest setting. The story could focus on the bond they form as they train together for upcoming battles. Another could be a fanfic that has Ash catch an Eevee and then they go on a journey to find different evolution stones for Eevee to choose from.
One possible plot twist could be that the legendary Pokémon start to lose their powers once caught by Ash. Another could be that there is a hidden cost or consequence to catching all of them that Ash doesn't initially realize.
One possible plot twist could be that Latios and Latias are actually under the control of a more powerful and evil Pokémon. Ash initially thinks he's caught them to protect them, but then discovers he has to fight against the real threat that has been manipulating them all along.
One common plot element is Ash's determination to catch Garchomp. He usually has to overcome various challenges, like Garchomp's strength and wild nature.
One typical plot point is how Nebby behaves before being caught. It could be scared, curious, or even a bit mischievous. Also, after the catch, the fanfiction might explore how Nebby adapts to being with Ash. Maybe it has trouble adjusting at first but then grows to trust Ash completely.
A common plot element is Ash's determination. He's always been a determined character in the Pokémon series, and in these fanfictions, that determination drives him to catch Necrozma. Another element could be the power struggle. Necrozma is a very powerful Pokémon, so there's often a back - and - forth between Ash's attempts to weaken it and Necrozma's attempts to resist.
Another theme is Eevee's evolution. Many fanfictions explore different ways Eevee could evolve and how that affects its relationship with Ash and their adventures. For example, if Eevee evolves into a Vaporeon, it might lead to underwater adventures. Also, the theme of friendship and loyalty is always there. Ash and Eevee rely on each other, and this is often a central part of the stories.
A common theme is growth. Both Ash and the Eevee grow as individuals. Ash becomes a better trainer, and Eevee evolves or becomes stronger. Another theme is friendship. The bond between Ash and Eevee is often explored deeply.
Another theme is growth. Ash might help Eevee evolve or Eevee might help Ash become a better trainer. For example, in some fanfictions, Eevee's loyalty gives Ash the motivation to keep going in tough battles. Also, the theme of friendship that turns into love is quite prevalent. They start as friends but as they share more experiences, their relationship deepens into love. It's really interesting to see how different authors explore these themes in different ways.