One possible reason could be a misunderstanding. Maybe a character in the fanfiction misinterprets Namjoon's actions. For example, if he was trying to do something helpful but it came across as interfering. Another reason might be jealousy. If Namjoon is achieving great things in the fanfiction world, other characters could be envious and lash out at him.
Perhaps in the fanfiction's plot, Namjoon has made a mistake that has a big impact on others. It could be something like accidentally revealing a secret that was supposed to be kept. This would understandably lead to someone yelling at him as it has put them in a difficult situation.
Another way he could react is with resignation. If he realizes that the person yelling at him is not going to listen to reason, he might just let them yell and not fight back. He could simply look down, shoulders slumped, and wait for the yelling to stop. This could also show his maturity in the face of unjust anger.
If this were a real situation, perhaps he was having a bad day and lost his temper. Sometimes people let their stress out in inappropriate ways.
Next, Namjoon could start to recover and decide to write a song about his experience. He might use the time he spent sick as inspiration, with lyrics about the care he received from the members and how it made him feel. The cute comic could show him scribbling down lyrics in a notebook, with the other members looking on with pride.
One possible scenario in this fanfiction could be that the other BTS members take care of Namjoon. They might bring him warm soup, his favorite books to read while he's sick in bed. Jin could be in the kitchen cooking up a storm to make sure Namjoon gets his strength back. Jimin and Taehyung might be by his side, telling him funny stories to cheer him up. Jungkook could be running errands like getting medicine. And Suga and Hoseok would be there to keep the mood light and positive around Namjoon.
One possible reason could be unrequited love. Maybe Natsu has feelings for someone who doesn't feel the same way about him. This could lead to his heartbreak as he realizes that his love is not reciprocated.
Maybe Tails was tinkering with Sonic's shoes or some other personal item without permission. Sonic values his stuff and his independence. If Tails was messing around with his things in an attempt to 'improve' them but instead caused a problem, Sonic would likely be angry.
One possible reason could be if Naruto in the fanfiction is being unfaithful to her. In the original series, their relationship is built on trust and love. So, if the fanfic portrays Naruto in a way that goes against that, Hinata might get mad.
One reason could be that the fanfiction often portrays the characters in a very different way from how he knows them. For example, if it changes their personalities too much, it might make Naruto feel like it's not the same team he belongs to. Another reason could be the overuse of certain plot devices in the fanfiction. Maybe every story he reads has the same cliché situations, like the team always getting into the same type of trouble in a very predictable way. Also, if the fanfiction focuses too much on relationships that Naruto doesn't see as important within the team, it could put him off.
One possible reason could be jealousy. Naruto is very powerful and some in Konoha might be envious. For example, some minor clans might feel that Naruto, as an outsider in a sense, gets too much attention and resources. Another reason could be fear. His Nine - Tails power is so immense that some might fear he could lose control and endanger the village, so they betray him to try and eliminate the 'threat' before it's too late.
Perhaps in the fanfiction world, there is some sort of magical or technological device that mutes Naruto. This could be part of a plot where an enemy uses this device to stop Naruto from using his inspiring speeches or to isolate him from his friends. By muting him, they can disrupt his normal way of communicating and leading, which is a key aspect of his character.