In 'female diablos x human fanfic', a frequent theme is the exploration of differences. Physical differences, cultural differences (if we consider the diablo to have its own 'culture'), and even differences in how they perceive the world. Another common theme is redemption. Maybe the diablo has a dark past and the human helps her to find a new path. And of course, the theme of connection - how two such different beings can form an emotional or even a spiritual bond.
I'm not sure specifically about 'female diablos x human fanfic' stories. However, you can try looking on some fanfiction websites like Archive of Our Own. There might be some unique takes on such a pairing there.
One common theme could be friendship that transcends species. Since a charizard is a Pokémon and a human is, well, human, the story might explore how they form a bond. Another theme could be adventure, where they go on quests together.
A frequent theme is the struggle for acceptance. The female yautja may face opposition from her own kind for getting involved with a human, and the human may also face skepticism from other humans. There is also the theme of transformation. The relationship often changes both characters. For example, the human may become more fearless and learn new skills from the yautja, and the yautja may develop more empathy. And love, of course, is a common theme. Whether it's a romantic love or a deep platonic love, it's central to many of these fanfics.
Another possible theme is the idea of acceptance. The human might have to accept the differences between themselves and the female Linoone, which is not only a Pokémon but also a female one. This could lead to a story about breaking barriers and understanding different species. There could also be a theme of protection, where the human protects the female Linoone or vice versa, depending on the nature of the story and the threats they face in the fictional world.
In 'female turian x human fanfic', the theme of adaptation often comes up. The two species have different physical and social characteristics, so the characters have to adapt to be with each other. For example, a human might have to get used to the turian's more rigid social structure. Also, the idea of finding common ground is important. They may discover shared values like loyalty or a love for exploration, which helps to strengthen their relationship. And there can be a theme of sacrifice, where one or both characters are willing to give up something for the sake of their relationship.
One common theme could be the power dynamic. Since the female is an elite, there might be exploration of how the male human deals with her status and power. Another could be a kind of 'fish out of water' scenario if the male is from a more ordinary background.
Another theme is the idea of acceptance. Since the human and the pokemon are different species, there is often a struggle for the characters to accept their feelings. They might worry about what others will think or if their relationship can even work. This adds an interesting layer of conflict to the story. In some fanfics, they have to overcome prejudice from other humans or pokemon. It's like a Romeo and Juliet situation in a way, but with different species.
One common theme could be adventure. The human male and female furry characters might go on an adventure together, facing various challenges. Another theme could be friendship that gradually develops into something more.
Love and acceptance are quite common themes. Despite their differences, the male human and the female monster fall in love. This shows that love can transcend physical and cultural differences. And acceptance comes in as they both have to accept each other's flaws and differences to make the relationship work.
One common theme is the clash of cultures. Orcs and humans usually have different ways of life in fantasy settings.