Some of them might be amused. They could find the different takes on their characters and stories quite entertaining. For example, Superman might chuckle at a fanfic that has him in a comical situation.
The Justice League's reaction to Young Justice fanfiction would be complex. They are used to their own official narratives. Reading fanfictions would expose them to alternative versions. Martian Manhunter, with his telepathic abilities, might be able to sense the passion and creativity of the fans behind the writing. But some, like Cyborg, might be more concerned with how accurately the technology in the fanfic is portrayed compared to his own understanding. And they all would have to grapple with the fact that the fanfictions are a form of the public's interpretation of their world, which could be both flattering and challenging.
Some members of Young Justice could be embarrassed. For instance, if there are romantic fanfictions about them that are a bit too cheesy or if their weaknesses are overly emphasized in a not - so - flattering way. But others might be really intrigued and want to explore more of what the fans think about them.
The Flash might initially be in denial. He's used to Batman always having a plan and his death would be a huge shock. He would then turn his speed into a tool for investigation, trying to find out exactly what happened. Green Lantern could feel a sense of loss but also be spurred into action, using his ring to try and prevent future tragedies like Batman's death. He might create constructs in Batman's memory to inspire the team.
They would probably be shocked at first. Fanfictions often contain wild and unexpected storylines.
They might be intrigued. The different takes on the MCU heroes and villains could capture their attention.
The Justice League as a whole would have a diverse range of reactions. Some members like the Flash would be all for it, seeing it as a fun exploration of Batman. Others like Wonder Woman might use it as a way to understand how the public perceives Batman's role in the League. And then there are those like Aquaman who might just shrug it off unless it directly affects his interests. The fanfiction could also potentially create some internal discussions within the League about how they are all portrayed in the public's imagination.
Some of them might laugh. They would see the creative and sometimes out - there ideas that fans come up with in the fanfiction. For example, if there's a fanfic where Oliver Queen teams up with a really strange character from the Arrowverse, it could be quite humorous to them.
They would be amazed. The Justice League is used to their own brand of super - powered battles, but Infinity War would show them a whole new level of cosmic warfare. Superman might be the first to jump into action, mentally preparing himself to take on Thanos if he was in that universe.
They'd likely be intrigued. Batman would study it for plot devices and character development. He might use some of the ideas in his own crime - fighting strategies. Superman would probably be entertained, seeing it as a new form of storytelling about a hero. Wonder Woman might view it as a cultural phenomenon and think about how it reflects on modern society's view of heroes.
Batman would probably be more critical. He'd analyze how the fanfiction portrays his detective skills and his relationship with the other members of the Justice League. He might not like it if the stories make him seem too soft or too brutal, as he has a very specific self - image.
Some might be amused, while others could be offended. It depends on how they are depicted in the fanfiction.