One idea could be that Bowser decides to give up his evil ways to win Princess Peach's heart in a more noble way. He starts doing good deeds around the Mushroom Kingdom, like helping to rebuild damaged areas.
Maybe in the fan fiction, Princess Peach gets tired of always being the damsel in distress. She secretly learns combat skills and challenges Bowser to a duel to end his constant kidnappings once and for all. And through this process, they start to understand each other better.
One idea could be that Peach initially marries Bowser out of a sense of duty to save her kingdom from constant attacks. But as time goes on, she discovers a different side of Bowser and they gradually develop an unexpected bond. For example, Bowser might show a softer side when it comes to their private moments together.
One idea could be that Bowser, in an attempt to win Peach's heart in a more unconventional way, decides to start a lemonade business. He makes the most amazing lemonade using magical lemons from his kingdom. Peach is initially skeptical but as she tries the lemonade, she starts to see a different side of Bowser. This could lead to a series of comical and heart - warming interactions between them.
One idea could be that Mario gets trapped in an alternate dimension where he has to find a way back to the Mushroom Kingdom and to Princess Peach. Meanwhile, Peach has to hold off Bowser's attacks on her own without her usual hero.
One idea could be a story where Peach and Bowser are forced to team up against a greater evil that threatens both the Mushroom Kingdom and Bowser's domain. They start off hating each other but gradually learn to respect one another's strengths.
Toad could be a great addition. He's always been Princess Peach's loyal servant. He could try to rescue her in his own bumbling way when Bowser kidnaps her, adding some humor to the story.
There could also be a fanfic where Bowser and Princess Peach are both transported to a different dimension. In this strange new world, they have to rely on each other to survive. As they face various challenges together, they start to develop a deeper understanding of one another. This could potentially lead to a romantic relationship or at least a strong friendship that changes their views on each other when they return to their own world.
One idea could be a story where Bowser and Peach have to team up to save the Mushroom Kingdom from a new, greater threat. This would force them to put aside their differences and work together, leading to a new understanding between them.
One interesting plot twist could be that Bowser actually saved Princess Peach from a greater threat in the past, which she has forgotten. This could add a layer of complexity to their relationship. Another could be that Bowser, in an attempt to win Peach's love, transforms into a more civilized and charming version of himself, but still struggles with his old, brutish nature.
One idea could be that Princess Peach discovers a hidden power within herself during the Showtime event that allows her to communicate with the spirits of the Mushroom Kingdom's past rulers. She uses this newfound ability to learn ancient secrets and protect the kingdom from a new, unexpected threat.
One common theme is redemption. Writers often explore the idea of Bowser being redeemed through his interactions with Peach. Another theme is the power of love, like if Bowser falls in love with Peach in a more sincere way rather than just lust for power. Also, friendship can be a theme where they become friends despite their differences.