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.
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.
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.
One way could be to start with Harry being somehow transported to the RWBY world. He could then use his magic skills to help the RWBY characters in their battles against the Grimm. For example, he could use spells like 'Stupefy' to stun the Grimm or 'Expecto Patronum' to ward off large groups of them.
For a start like 'The sound of a lone howl echoed through the empty streets.', you could start by setting the scene more. Describe the empty streets, how desolate they look. The main character hears the howl and decides to follow it. Along the way, they might discover that there's a werewolf in the town. But the werewolf is not what it seems. It's actually a cursed person who needs help. The character then tries to find a way to break the curse, and this leads to a series of events where they search for an ancient spellbook or a magic item that can reverse the curse, facing other challenges like other superstitious townsfolk who want to kill the werewolf without knowing the truth.
One way could be to make the ants the main characters. They live in a world that is filled with elements of the long scary story. For example, they might be in a forest that is haunted by some unknown evil. The long part of the story could involve their journey through different parts of this spooky forest to find a new home.
First, you need to expand on the central secret idea. For instance, if your secret idea is a hidden treasure map. You start by thinking about where the map was found, who might have hidden the treasure, and why. Then, you create characters. Maybe a young adventurer who discovers the map by accident. Next, add conflict. There could be an evil villain who also wants the treasure. With these elements, you can start weaving them together to form a full - fledged story.
Perhaps there is a magical artifact that can only be activated or controlled by speaking a special incantation in a very precise way. Hermione is then tasked with figuring out how to 'use her tongue' to perform this task. Along the way, she might face challenges from other characters who also want to use the artifact for their own purposes, creating a conflict - driven plot.
First, introduce a character in a corporate environment who is known for their charm and allure, like a marketing executive. This person could start using their 'thirst trap' qualities, such as being confident and stylish, to gain an edge in the corporate world. Then, they meet another character, perhaps a rival from a different company. At first, it's a competitive relationship, but gradually, they start to see the real person behind the corporate facade and fall in love.
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.
To develop it, you could start by creating characters that represent x and y. Let's say x is a group that values art and heritage deeply and y is a group focused on technological progress. The culture war could be about the struggle for resources and recognition in a society. The love story might begin with a chance meeting at an event that bridges the two cultures. As the story unfolds, the lovers have to deal with the disapproval of their respective groups due to the culture war, but their love overcomes these obstacles in the end.