The Bat - family would be very worried. Alfred, being like a father figure, would be constantly at Batman's side, making sure he takes his medicine and rests. Robin would be eager to prove himself and take on more responsibilities in protecting Gotham in Batman's absence.
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.
Inuyasha may become uncharacteristically gentle. He'll softly speak to Kagome, asking how she feels. His actions are driven by his deep - seated feelings for her. He might even share some of his own insecurities with her while she's sick, like how scared he is of losing her. He'll also be on high alert for any danger, ready to defend her at a moment's notice.
Alfred reacts with calm efficiency. He quickly assesses Batman's injuries and starts to take care of them. He doesn't panic because he knows Batman needs him to be strong.
In many fanfics, the Bat Family is often devastated. Bruce might be filled with guilt, blaming himself for not being able to protect Jason. Dick could be angry and determined to find out who was responsible. Tim might feel a sense of loss and also a strange connection to Jason, as he took on the Robin mantle after him.
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.
Batman would probably isolate himself at first. He'd retreat to the Batcave to analyze the situation. He might feel a sense of guilt, thinking he should have seen the betrayal coming. After that, he'd start planning his counter - move. He'd use his vast resources and knowledge to expose the truth behind the betrayal and take down whoever is behind it.
Alfred would probably be the first one to take care of him. He's always there for Batman.
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.
First, know the characters well. Read the comics or watch the movies to understand their personalities and backstories. Then, come up with an interesting concept like a new threat to Gotham or a change in the family dynamic.
Batman might become more brooding. He could withdraw from the people around him, like Robin or Commissioner Gordon.