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.
In these fanfictions, the author has the freedom to explore new storylines. They can create adventures that are specific to this pairing. For example, how Ash and the anthro Lopunny interact in a world where Pokemon have more human - like qualities. It also allows for exploring different emotions and character developments that might not be possible in the canon series. Plus, the anthro Lopunny can bring in her own set of characteristics and abilities that add depth to the story.
A common theme is friendship. The male trainer and Lucario form a strong bond that helps them through various challenges. Another theme could be growth, both for the trainer in terms of becoming a better Pokémon trainer and for Lucario in evolving its skills.
Love and connection are perhaps the most prominent themes. The stories usually explore the unique connection between a human (the reader) and the female Lucario. It can be a platonic love at first, but often evolves into a deeper, more romantic kind of love. There are also themes related to the Lucario's unique abilities and how they are used to protect or help the reader in different situations.
One common theme could be friendship evolving into something more. Since Lucario and Mew are both Pokémon, they might start as friends or allies and then develop deeper feelings.
Finding good 'lucario x mew mew she fanfiction' can be a bit of a hunt. First, think about what kind of story you're interested in. Do you want a romantic story, an adventure with them together, or something else? Then, when you search on fanfiction platforms, use specific keywords related to the type of story you desire. For example, if you want a romantic story, you could add 'romance' to your search terms. Also, look at the ratings and reviews of the stories to find ones that are well - received.
There might be some fanfic communities on social media platforms dedicated to Pokémon. You could join those groups and ask for recommendations regarding 'male trainer x lucario fanfic'. People in those communities are often very passionate about Pokémon fanfiction and might be able to point you to some great reads. Another option is to look for Pokémon fanfic anthologies, either in print or digital form, which could potentially contain stories about this pairing.