It's possible. The world of fanfiction is vast and diverse. Eevee is a popular Pokémon, and with that popularity comes a large number of fan - created stories. While the idea of an eevee being pregnant in a fanfiction might seem a bit unusual, it's not out of the realm of possibility given the creative nature of fanfiction writers. They can take the basic concept of eevee and build all sorts of unique stories around it, including ones where eevee is pregnant.
Well, often there's a theme of change. The pregnant Eevee has to adapt to physical and emotional changes. There can also be a theme of community. The other Pokémon around the pregnant Eevee might form a sort of community to support it. For instance, they could help gather food or keep the area safe. In some fanfictions, the theme of mystery might also be present. There could be something special or unique about this particular Eevee's pregnancy that the characters need to figure out.
In the Pokémon world, such a concept goes against the nature of these fictional creatures. Pokémon are generally not depicted in this way in official or most fan - created content. So, it's very unlikely that there is a legitimate fanfiction with such a plot.
You could start by looking on Archive of Our Own. It has a large collection of fanfictions on various topics, including Pokémon - related ones. Just use their search function and type in relevant keywords like 'eevee pregnant'. However, there's no guarantee that you'll find exactly what you're looking for.
One popular pregnant Eevee fanfiction is 'The Eevee's New Beginning'. It focuses on an Eevee's journey during pregnancy and how it copes with the changes. Another one could be 'Pregnant Eevee's Adventure' which has interesting plotlines about the Eevee's interactions with other Pokémon during this special time.
It's against the family - friendly nature of Pokémon. Pokémon is aimed at a wide range of audiences, including children, and such a plot would be inappropriate.
In fanfictions, they often portray their emotions through body language. For example, the male Eevee might wag its tail more when it's around the female Eevee it likes. The female Eevee could nuzzle up to the male to show affection.
There are fanfictions where male and female Eevee love is depicted in a more comical way. For instance, the female Eevee is always chasing the male Eevee around because she has a crush on him, but the male Eevee is a bit clueless at first. As the story progresses, he finally realizes her feelings. And then there are those that delve into their different evolutions and how that might affect their relationship, like if one evolves into a Vaporeon and the other into a Jolteon, and how they still manage to love each other despite their differences.
The male Eevee might start off as a loner. But when he meets the female Eevee, he begins to change. He could develop a sense of loyalty towards her. The female Eevee, on the other hand, could be very social and introduce the male Eevee to new friends in the Pokémon community. This new social circle could put pressure on their relationship in some ways, but also help them grow. For example, they might have to deal with jealousy from other Pokémon who like either the male or female Eevee. Through these experiences, their characters can be further developed.
To write a compelling Eevee starter character, first give it a distinct personality. For example, it could be a curious Eevee that is always getting into trouble because it wants to explore. Second, give it a unique backstory. Maybe it was abandoned by its previous trainer and is now a bit shy but determined to prove itself. Third, show its growth throughout the story. As it faces challenges, it becomes more confident and learns new skills.