No. Creating fanfiction that involves sexual content about Pokémon characters is not appropriate. Pokémon is a franchise aimed at a wide range of audiences, including children, and such content goes against the family - friendly nature of the brand.
Another appropriate theme could be them exploring a new and mysterious region in the Pokémon world. They might encounter new Pokémon species, discover ancient secrets, and rely on each other's strengths to overcome obstacles, which would be a positive and engaging story.
One great 'Pokemon Lucario and Lopunny fanfiction' is 'The Bond Beyond Types' on FanFiction.net. It explores the unique relationship between Lucario and Lopunny in an adventure - filled story.
First, think about the relationship between Lucario and Lopunny. Decide if it's a friendship, a rivalry, or something more. Then, create a plot. For example, they could go on a quest to find a rare Pokemon or a powerful item. Don't forget to give them distinct personalities based on what we know of them from the Pokemon games and anime.
There's a fanfic called 'Lopunny's New Friend'. In this, the oc is a young trainer who discovers an injured Lopunny. They form a strong bond as the oc nurses the Lopunny back to health and then they start exploring the Pokémon world together. It's full of heartwarming moments and exciting battles against other Pokémon.
In a well - written oc x lopunny fanfic, the dialogue between the oc and Lopunny (even if it's more of an implied communication in the Pokémon's case) should be natural. It can't be just dry statements. And the pacing of the story should be right. Not too slow that it bores the reader, and not too fast that important details are missed. There should also be some emotional depth, like when the oc and Lopunny face a difficult separation or a dangerous situation together, which makes the reader care about their relationship.
A possible fanfiction could focus on a male character who discovers a lost and injured female Lopunny. He takes her in and nurses her back to health. As she recovers, they form a deep connection. They start exploring the Pokemon world together, with Lopunny learning new moves and the male character learning more about Lopunny's species. It could be a heart - warming story of friendship and mutual growth.
One idea could be a story where the male reader is a trainer who discovers a female Lucario in the wild. They form an instant bond and start a journey together, facing various challenges in battles and in understanding each other's emotions.