One possible scenario could be that Pikachu is exposed to a strange type of energy. This energy mutates its genetic structure, slowly transforming it into a human form. At first, Pikachu might be confused and scared, not understanding its new body. But as time passes, it starts to learn about human ways, like walking on two legs and using its hands to pick things up.
Pikachu might find it difficult to communicate at first. Since it was used to making 'Pika - pika' sounds, it would have to learn human languages. It could start with simple words and phrases, and as it becomes more proficient, be able to have complex conversations. For example, it might try to explain to Ash how strange it feels to have fingers instead of paws.
Most likely, this is a very niche and perhaps even inappropriate concept for fanfiction. The Pokémon world and the human world are kept quite distinct in the official lore, and crossing those boundaries in such a way as a 'pregnant' scenario goes against the general spirit of the Pokémon franchise. So, it's doubtful there are many, if any, proper fanfictions on this.
Well, one possible interpretation could be a very strange and unique take on the relationship between Ash and Pikachu. Maybe it's a metaphorical exploration of their deep bond in a really extreme way. But this is a very odd concept.
No. It is highly unethical. Pikachu is a fictional creature from the Pokémon franchise and humans have a different biological nature. Writing about such an impossible and inappropriate relationship in a sexual context, as in 'lemon' fanfiction, violates basic ethical norms regarding appropriate content and respect for the source material.
They could start by trading Pokémon - related stories. The male human might tell Ash about his first encounter with Pikachu, and Ash could share his own adventures. As they talk more, they find common ground and start to respect each other. Then, when they face a common enemy, like a Team Rocket - like organization trying to steal Pikachu, their relationship evolves into a strong friendship.
No, in the real world, there's no way for a Pikachu and a human to get pregnant. Fanfiction, especially the 'lemon' variety, sometimes takes very wild and unorthodox ideas. But we need to remember that it's all fictional and often not in line with common sense, biology, or ethical standards. This kind of fanfiction might be written for shock value or to explore very extreme and often inappropriate ideas within a fictional and often unregulated writing space.
Maybe the male human is from a different region and has a Pikachu with a unique ability. Ash becomes intrigued by this and they start to travel together. Along the way, they discover that their combined skills and the power of their Pikachus can help solve mysteries about some rare Pokémon. Their friendship grows as they overcome challenges together.
There is no such fanfiction that is appropriate or ethical. Pokémon are fictional creatures and the idea of a human and a Pokémon in such a situation violates the nature and ethics of the Pokémon universe. So, you won't find it in any legitimate fanfiction platforms.
One idea could be a story where the human Pikachu and the reader are on a journey to discover a new type of Pokémon. Along the way, they face various challenges like difficult terrains and other Pokémon battles. Their relationship grows as they rely on each other for support and survival.