Well, Betty will be super worried. She's always had a soft spot for Archie. She might skip her own activities to stay by his side, constantly checking his temperature and making sure he's comfortable. Jughead, on the other hand, will try to keep things light. He'll tell Archie stories about the latest strange things he's seen in Riverdale to distract him from his illness. Veronica will be more of the practical one. She'll call in doctors or specialists, using her family's influence to ensure Archie gets the best care possible. All in all, his friends will rally around him.
The plot might involve Archie getting sick due to some sort of mystery in Riverdale. For example, there could be a strange virus going around that only affects certain people. Archie's sickness could be the starting point of an investigation. His friends, being the curious and caring bunch they are, start looking into what's causing it. This could lead to uncovering secrets in the town that were previously hidden. Also, Veronica might use her family's resources to try and find a cure for Archie.
His friends would most likely be very concerned. They would probably bring him things like food and medicine. TK might pray for his quick recovery.
Olaf would try to make Anna laugh. He would tell his silly jokes and do his goofy dances. He would also try to keep Anna warm with his carrot nose. He might even build a small snowman inside the room to keep Anna company when everyone else is busy.
Raven would probably be the first to sense that something was wrong with Beast Boy. She'd be quiet about it at first, but she'd start keeping a closer eye on him. Maybe she'd make him some herbal tea that she believes has healing properties.
His friends would most likely be very worried. They would gather around him, trying to figure out what was wrong. Percy might use his water powers to cool Leo down if he had a fever. Annabeth would be researching in the library, looking for any information on demigod illnesses. Hazel could use her powers to sense if there was any dark magic involved in Leo's sickness.
His other friends like Shikamaru would think of the most practical solutions. He might calculate the risks of continuing the mission with a sick Naruto and come up with a plan. Maybe he'd suggest splitting the group, with some staying to take care of Naruto and others proceeding with the mission - related tasks that can't be postponed.
In most 'Naruto gets sick' fanfics, his friends are very concerned. For example, Sakura will immediately start using her medical skills to diagnose and treat him. Sasuke, although he may not show it outwardly as much, will stay by Naruto's side and keep a watchful eye. Shikamaru might come up with plans to make Naruto more comfortable during his illness. And Hinata, she would be really worried and would probably bring Naruto some home - cooked food to help him regain his strength.
Well, consider Hamilton's son. He would be scared and confused, not fully understanding what's happening to his father. He might try to be brave and do little things to make Hamilton feel better, like drawing pictures for him. Hamilton's friends in the military, like Laurens, if he were still alive in this fanfiction, would be ready to defend Hamilton from any potential threats during his illness. They would be on high alert because they know Hamilton has enemies. And the ordinary people who have been inspired by Hamilton's ideas would be praying for his recovery and sending well - wishes, which would add to the sense of Hamilton's importance in the community.
Sakura, being a medical ninja, would immediately start examining Naruto. She'd be very worried and use all her skills to try and diagnose the illness. Sasuke, on the other hand, might not show his concern openly but would be constantly on edge. He might secretly look for ways to help Naruto get better. Shikamaru would probably start thinking of strategies to keep the village safe while Naruto is sick.
Damian probably reacts with frustration. He's used to being strong and capable, so being sick makes him feel vulnerable. He might try to push through it at first, not wanting to admit that he's unwell.