The Karma Seal can change Naruto's appearance. In some fanfictions, it might give him a more menacing look with strange markings spreading across his body.
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.
One interesting Naruto Karma Seal fanfiction could be about how the Karma Seal affects Naruto's relationships differently. For example, it might create a rift between him and some of his friends who fear its power.
It could be a rogue ninja who has a personal vendetta against Boruto's family. This ninja might have caused harm to Boruto's father Naruto in the past, and now Boruto is determined to make him pay.
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.
Well, maybe Boruto's family or friends are hurt by a powerful enemy. So he decides to train hard and seek revenge. He might travel to different places to learn new jutsu and gather allies along the way.
Maybe in the fanfiction, Katsuki has always been overconfident and underestimated his opponents. The bad karma could be that he faces a powerful enemy who completely outmatches him. He then has to struggle not only with the physical threat but also with the psychological blow of his own hubris. This would force him to re - evaluate himself and his actions.
Maybe in the fanfiction, Boruto is abused by a powerful and evil villain who wants to get back at Naruto by hurting his son. The villain could use dark jutsu to physically and mentally torture Boruto.
There shouldn't be any such fanfiction. Boruto and Himawari are siblings in the Naruto universe, and creating a story about them in such a way goes against the basic values of family and propriety. It would also be unacceptable to a large number of fans who respect the original work.
One possible plot could be that Boruto and Hinata have a deep emotional bond that develops over time. They face many challenges in the Hidden Leaf Village together, which brings them closer. As a result of their love and closeness, Hinata becomes pregnant, and then they have to deal with the reactions of their family and friends, like Naruto's reaction as Boruto's father and also how the village will perceive this new development.