A common theme is the exploration of the Pokémon world from a different perspective. As an Eevee, Ash sees things in a new light. He experiences the Pokémon world on a more intimate level, like understanding the language of Pokémon better. There's also the theme of adaptation. He has to quickly adapt to his new physical form, which includes learning to move, run, and use his new Eevee - specific abilities.
The plot might involve Ash turning into an Eevee and being found by a group of Eevee and their evolutions. They initially view him as an oddity since he has the memories and some of the behaviors of a human. Ash, as an Eevee, could then learn new skills from his new companions and use his knowledge from being a human trainer to help the group in various situations, such as finding food sources or avoiding predators.
I'm not sure of the exact name, but there's a fanfiction where Ash turns into an Eevee and gets caught by a trainer. This one is really unique as it shows the Pokémon world from the perspective of a captured Pokémon. Ash has to use his knowledge as a human - turned - Eevee to escape and also tries to communicate with the other Pokémon in the trainer's team. It's a great read for those who like a different take on the 'Ash turns into an Eevee' concept.
His other Pokémon like Charizard would be completely bewildered. Charizard might initially think that this Eevee is just some random Pokémon near its territory. But when it senses something familiar about the Eevee, it would be hesitant and curious. It could try to communicate in its own way, like using small bursts of fire to get the Eevee's (Ash's) attention. The Pokémon that Ash has a closer bond with would be more determined to figure out what's going on and how to help him.
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 great 'Ash starts with Eevee' fanfiction is 'Eevee's Adventure with Ash'. It shows Eevee evolving in unique ways under Ash's guidance. Another one could be 'Ash and Eevee: A New Bond' which focuses on their initial meeting and how they form a strong connection that helps them in battles.
Well, if it's a lemon fanfiction involving Ash Ketchum and Eevee, it's likely to be a creative and perhaps out - of - the - ordinary story. Lemon in fanfiction often implies a more adult - themed or romantic - leaning content, but in a non - official and fan - created context. However, this kind of fanfiction might not be in line with the original spirit of the Pokémon franchise which is more family - friendly.
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.
In an 'Ash turns into Latios' fanfiction, perhaps Ash is turned into Latios as a way to better understand the Pokémon he has befriended. As Latios, he might be able to communicate with other Pokémon on a deeper level. For example, he could learn the secrets of legendary Pokémon that have always been a mystery. His friends, like Pikachu and Misty, would initially be shocked but then have to figure out how to help him reverse the transformation or support him in this new form.
In this kind of fanfiction, we might see Ash and Eevee in situations that are not part of the normal Pokémon narrative. For example, their relationship could be explored in a more complex way. The 'lemon' aspect may bring in elements like deeper feelings, perhaps some jealousy or possessiveness that wouldn't be found in the regular Pokémon series. However, this also means it might not be as accessible to younger fans who are used to the more straightforward Pokémon - trainer relationships.