The long - term consequence might be that Sonic has to completely redefine his role in his world. Instead of being the front - line hero who dashes into danger first, he might become more of a strategist, using his brain and his remaining senses to plan attacks. His relationships with his enemies could also change. Some enemies might see his blindness as a weakness and target him more, while others might respect his new - found vulnerability and leave him alone. And his friends would have to take on more of a protective role, which could strain some of his relationships as he might not like being 'protected' all the time.
In a fanfiction like 'The Blinded Hedgehog', Sonic is blinded by a toxic gas. This forces him to slow down and re - evaluate his fighting style. His friends, especially Tails, use their skills to assist Sonic in his time of need and they all work together to find a cure for his blindness.
Another possibility is a corrupted version of one of Sonic's friends. Maybe through some dark influence, like an evil Chaos Emerald, a friend turns on Sonic and blinds him. This would add an extra layer of drama as Sonic has to deal not only with his blindness but also the betrayal of someone he trusted.
His friends would likely be very concerned. Tails, for instance, would probably immediately start working on some kind of device to help Sonic regain his sight or at least make his life easier. He might create a pair of goggles with special sensors that can detect obstacles. Amy would be very emotional and would offer a great deal of emotional support, constantly staying by Sonic's side to make sure he's okay. Knuckles might be a bit more practical, offering to train Sonic in new ways of fighting that don't rely on sight so much.
I'm not sure specifically as there could be various interpretations in such a fanfiction. Maybe Metal Sonic sets Sonic up in a way that makes Sonic look bad to the other characters, perhaps by faking some evidence or causing chaos and making it seem like Sonic's fault.
Positive Sonic fanfiction could be about Sonic mentoring the younger characters like Tails and teaching them important life lessons. Or it could be about Sonic and his friends having to solve a mystery in their world, like a strange disappearance of an important item or character. Fanfictions that show the characters growing and evolving in positive ways, such as Amy becoming more confident in her own abilities, are also excellent alternatives to inappropriate fanfiction themes.
Obviously, Sonic and Metal Sonic are the main characters. Sonic is the one being framed, and Metal Sonic is the one doing the framing.
Sonic would probably be very shocked at first. He trusts Amy, so her betrayal would be unexpected. He might initially try to talk to her to understand why she did it.
It could be Dr. Eggman. He's always been after Sonic and trying to defeat him. Experimenting on Sonic could be his new way to find Sonic's weaknesses or to gain his powers for himself.
It could make some fans uncomfortable. Since Sonic is a family - friendly character, this type of dark and negative fanfiction can create a negative atmosphere in the community.
One possible plotline could be Sonic struggling to come to terms with his new robotic parts. He might face challenges in his speed or his usual acrobatic abilities and have to relearn how to move and fight. For example, his robotic parts could malfunction at crucial moments.