Luigi would probably be very surprised at first. He might be a bit confused, but then he would support his 'sister' Mario. Princess Peach would be delighted. She could finally have a female friend who has all of Mario's skills. Bowser might not even notice at first, thinking it's just another ploy by Mario. But when he realizes it's a real transformation, he might be a bit more hesitant in his attacks, not sure how to deal with this new female Mario.
The Toads would be quite shocked. They are used to seeing Mario as a male hero. But they would quickly adapt and start referring to Mario as a girl. Yoshi might not really understand the concept of gender transformation, but he would still recognize Mario's scent and be his loyal friend. Donkey Kong would probably have a good laugh at first, but then respect Mario's new form and still see him as a worthy opponent or friend depending on the situation. And the Koopa Troopas might be a bit more scared of this new female Mario, thinking she has some new, unknown powers.
Well, one possible plot could be that Mario touches a magical item in the Mushroom Kingdom. This item has the power to transform him. As he turns into a girl, he discovers new abilities. Maybe he can now access areas only females can in the kingdom. He also has to deal with how his friends like Luigi react to his new form.
Luigi could be an important character. He might notice the shy girl before Mario does and tries to encourage her to talk to Mario. Or, Toad could be there as a friendly sidekick, helping the shy girl get used to the new environment in the Mushroom Kingdom. He could also give her tips on how to overcome her shyness based on his own experiences.
The fanfic has also led to more discussions within the Mario fandom. Fans debate about the plausibility of the relationships and storylines in the 'bowsette and mario' fanfics. This kind of interaction keeps the fandom alive and engaged, as everyone has their own opinion on how the Mario universe can be expanded or re - imagined.
One interesting plot could be Mario, now as a girl, having to navigate the Mushroom Kingdom in a different way. Maybe she discovers new powers that come with her new form and uses them to save the kingdom from a new threat.
Another possibility is that a group of Koopa minions could be the main antagonists. They might be under the orders of Bowser, but they have their own little schemes going on. They could target Mario - turned - girl because they think she'll be an easier target in her new form, but they are in for a big surprise when she shows her strength.
Princess Peach would be a great addition. She could be in trouble as usual, and Mario and Luigi have to rescue her. But this time, she could also play an important role in helping them solve a mystery or defeat a powerful enemy. For example, she might have some knowledge about an ancient artifact that the brothers need.
Mario's dream in the Super Mario World could be about him flying over all the levels without any enemies. He soared above the green hills, the lava pits, and the ice worlds. He could see all the hidden power - ups and coins from above. In his dream, he just had to reach out and grab them all. He was having so much fun flying around that he didn't want to wake up.
Mario is most likely the main character in 'dark star mario fanfic'. Since it's a Mario - centered fanfic, he would be the central figure dealing with the events related to the dark star.
Princess Peach could be another main character. She might be at the camp for some diplomatic visit or just for a fun break, and she often adds a touch of elegance and sometimes needs rescuing or helping in the camp - related adventures.
Well, clearly Mario and Bowser are the main characters. Mario, the heroic plumber, is always ready to save the day. And Bowser, the big, bad turtle - like villain who usually causes trouble for Mario and his friends.