Well, perhaps it involves Luigi getting some strange illness that no one in the Mushroom Kingdom has seen before. So, Mario and Princess Peach have to search for a cure all over the place. They could meet new characters during their search who either help or hinder them in their quest to make Luigi well again.
Mario would most likely be a main character too. He's Luigi's brother, so he'd be there to take care of him or at least be really worried about him. Princess Peach could also be a main character. She might visit Luigi when he's sick and bring some kind of magical item that could potentially help him get better.
Maybe it's a new villain in the fanfiction. This villain could be after Luigi because he thinks Luigi has some sort of special power or knowledge. So the villain kidnaps Luigi in a very sneaky way, like using a magic spell to put Luigi to sleep first and then whisking him away to a secret lair hidden deep in a dark forest.
Yoshi could also be the rescuer. Yoshi has his long tongue that can be used to grab things from a distance. He could use it to pull Luigi out of a locked cage or something. And Yoshi is very fast and can jump high too. So he'd be a great candidate to go on a rescue mission for Luigi.
In addition to his family and friends, the medical ninja in the village would be involved. They would be the ones to accurately diagnose Boruto's condition. Shizune, for example, could come and check on him, using her vast medical knowledge. And the other young medical ninjas might learn from this case, as Boruto's illness could be something new or unusual, so they would be eager to assist and gain experience while taking care of him.
Seth could be the one to help her. As her brother, he would be very concerned and might use his own knowledge of Fablehaven and its secrets to try and find a cure. He could also enlist the help of some of the friendly magical creatures they've befriended, like the fairies or the satyrs.
His teammates, Sasuke and Sakura, would surely be involved. Sasuke, although he may not show it as much, still cares about Naruto. He would keep an eye on Naruto's condition, and if there was any sign of danger, he would be ready to protect him. Sakura would be more hands - on with the medical care, checking his temperature, giving him medicine, and making sure he rests properly.
Sango could also take care of Kagome. As a strong and kind - hearted woman, she would know how to nurse Kagome back to health. She might use her knowledge of herbs and remedies to make Kagome feel better. Plus, she would offer emotional support to Kagome during her illness.
In the 'Boruto Gets Sick' fanfiction, Boruto might experience various symptoms like a high fever, weakness, and coughing. His friends and family would likely be worried about him. They would probably take care of him, bring him medicine and try to make him comfortable.
The following are a few recommendations for novels where the male lead gets jealous and falls ill: " Forced Subjugation ": The male protagonist displayed extreme possessiveness and jealousy. He even hid the protagonist and did not allow anyone to meet him. 2. " Medical Beauty: The Evil Concubine of the Sick and Delicate Prince ": The male protagonist is paranoid and has a strong jealousy plot towards the female protagonist. These novels all had plots where the male lead was jealous and fell ill, so they were suitable for readers who liked this type.