In the fanfiction, Biy turning into Espeon could mean a shift in its place in the Pokemon ecosystem. Espeon is a more evolved and powerful form. So, it might be targeted by stronger predators or rival Pokemon. Socially, among other Pokemon, it could face isolation as it is no longer the same as before. Also, its diet might change, which could affect the availability of food resources in the area where it lives.
Well, if Biy turns into Espeon, there could be a whole lot of emotional consequences. Biy might feel confused and lost at first, not understanding its new body and powers. It could also experience a sense of loneliness as it may no longer fit in with its old group. From a trainer's perspective, if Biy had a trainer, the trainer might have to adjust their training methods. Espeon requires different training techniques due to its psychic abilities. And in the grand scheme of the fanfiction's world, Biy's transformation could set off a chain of events. For example, it could inspire other Pokemon to seek out similar transformations, or it could attract the attention of powerful organizations that are interested in studying or controlling such transformations.
Well, it could be due to a psychic bond. Suppose there's a strong psychic Pokemon or a powerful psychic trainer in the fanfiction. They might form a connection with Biy. Since Espeon is a psychic - type Pokemon, this bond could gradually change Biy's form into that of Espeon. The psychic energy shared between them could be the catalyst for this transformation, which would make for an interesting story arc.
One consequence could be that Ash loses his human identity to some extent. His friends might not recognize him at first, and he would have to figure out how to communicate that he is still Ash inside. Also, his Pokémon might be confused about their trainer's new form.
To write a compelling Espeon character, first focus on its psychic abilities. Describe how it uses telepathy to communicate with other Pokemon and its trainer. For example, it could send thoughts to its trainer during battles to suggest strategies. Also, give it a distinct personality. Maybe it's a bit mischievous and likes to play pranks on other Pokemon using its powers. Another aspect is its loyalty. Show how it would do anything to protect its trainer or its friends.
Maybe it would be a story where Biy, a normal character, suddenly discovers he has the powers of a Pokémon. He could start his journey to explore the Pokémon world, meet other trainers, and compete in battles.
Well, a great storyline might be Espeon getting involved in a time - traveling adventure. It could end up in a different era of the Pokemon world and have to adapt. Maybe it meets ancient Pokemon and has to use its talking ability to negotiate with them. Also, a story where Espeon is on a quest to find a rare crystal that enhances its psychic powers. Along the way, it meets various challenges and makes new friends. And then there's the idea of Espeon being part of a Pokemon detective story, using its intelligence and talking skills to solve Pokemon - related crimes.
The plot could involve Ash stumbling upon an Espeon that has lost its memory. Ash tries to help it regain its memories. Along the process, Espeon starts to remember bits and pieces which lead them to different locations. These places hold secrets and also some powerful Pokémon. Ash and Espeon team up with his other Pokémon to uncover the secrets and protect the area from villains.
Since Espeon is often seen as an elegant and intelligent Pokémon, it might influence the behavior of Ash's more rambunctious Pokémon. It could teach them to be more strategic and calm. On the other hand, the other Pokémon might also introduce Espeon to a more fun - loving and adventurous side of life, changing Espeon's somewhat reserved nature a bit.
First, you need to define who Biy is. Is he a human, an alien, or something else? Then, decide how the transformation into the Pokémon world occurs. After that, you can start building the plot around Biy's adventures in the Pokémon world, like his first encounter with a Pokémon, his first battle, etc.
One consequence could be that Naruto loses some of his humanity. If he is constantly seen as a weapon, he might start to view himself in that way too. This could lead to problems in his relationships with his friends and allies as they might start to fear or be cautious around him.
One consequence could be that Harry is ostracized by some in the wizarding community who fear or misunderstand shifters. This would isolate him and make his life more difficult.