You can develop Wario by showing his softer side. Maybe he has a hidden love for cute things like small Toads. For Waluigi, explore his insecurities. He's often seen as the sidekick, so show how he wants to prove himself. They can develop together by having them share their dreams and fears with each other during a long journey.
One aspect of Waluigi's sad story is his role in the games. He is often used as a comical villain, but this also means he's not taken very seriously. In the Mario Party games, for example, he's there to disrupt the fun for the other characters. But he doesn't get to have real relationships or emotional depth like Mario and Luigi. He's just a tool for creating chaos and competition, which can be seen as a sad existence in the context of a story - rich franchise.
A 'waluigi x rosalina fanfiction' could be about exploring an unexpected relationship between the two characters. It might involve how their different personalities interact. For example, Waluigi is often portrayed as a bit of a mischievous character, while Rosalina has a more serene and maternal quality. In the fanfiction, the writer could create scenarios where Waluigi tries to impress Rosalina in his own clumsy way, or Rosalina helps Waluigi to become a better version of himself. It could also be set in different locations within the Mario universe, like on Rosalina's Comet Observatory or in one of the many kingdoms that Waluigi has visited during his adventures.
I'm not entirely sure about the existing 'god x waluigi fanfic' but generally, fanfics in this vein could be quite unique. It could be a story where God is a character in the Waluigi - centric universe. Waluigi might be constantly trying to impress God or seek his approval. This could lead to situations where Waluigi tries to outdo his rivals in a more spiritual or god - influenced context, like in a competition of good deeds or something similar.
The contrast between the two characters makes it appealing. Waluigi is a bit of a goofy, scheming character, while Rosalina is elegant and mysterious. When combined in a fanfic, it creates an interesting dynamic.
One popular 'waluigi x luigi fanfiction' is 'The Unlikely Bond'. It explores an alternate universe where the two characters have to team up against a common enemy. It's full of interesting character interactions and some really cool action scenes.
Often, there's a theme of redemption in these fanfictions. Waluigi, who is usually portrayed as a bit of a villain, may find redemption through his relationship with Luigi. Also, the theme of self - discovery is quite prevalent. As they interact, both characters learn more about themselves and their place in the Mario universe. There can also be a theme of overcoming differences, as they are very different characters in terms of appearance, behavior, and motives.
Another theme is friendship. Despite their differences, the fanfictions usually explore how they can form a bond. This could be because they are both related to Mario in different ways, and they find common ground in that family connection. They learn to accept each other's quirks and work together.
The main characters are, as the title suggests, Waluigi and Daisy. Waluigi is often portrayed as the more mischievous or underappreciated character in the Mario universe, while Daisy is the princess of Sarasaland. In the fanfic, their interactions and relationship are the focus.
One common theme is the discovery of Waluigi's true self. Since he's often portrayed as a bit of a villain or an outcast in the Mario universe, many fanfictions focus on the reader helping him show his better side.