One possible plot could be that a group of evil Decepticons steal Bumblebee because they know he has some valuable information stored in his memory banks. The Autobots then launch a rescue mission to get him back. They might face various challenges and battles along the way.
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.
In some fanfictions, it could be an unknown alien species. They might have detected Bumblebee's unique energy signature and decided to take him to study his technology or abilities. This could lead to all sorts of interesting adventures as Bumblebee tries to communicate with them and find a way to escape.
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.
One idea could be that Bumblebee is taken by a group of Decepticons who plan to reprogram him. Another could be that he's taken by a secret human organization for study. Maybe he's taken by a powerful alien race to use his abilities for their own purposes.
The author can make it engaging by focusing on the emotions. For example, showing how the other Autobots are worried and how Bumblebee feels lonely and weak. Also, by creating a sense of mystery around his illness. Is it a new virus? Or something the Decepticons did? Another way is to have some action in between. Maybe the Autobots have to fight off the Decepticons while also trying to take care of Bumblebee.