Tails would probably be very helpful. He'd use his intelligence to make sure Amy has a comfortable pregnancy, like creating special devices for her. Knuckles might be a bit awkward at first but would ultimately be very protective. He'd stand guard to make sure no harm comes to Amy and the unborn baby.
Tails would probably be really excited. He'd be the helpful uncle, always ready to use his mechanical skills to make cool toys for the baby. Knuckles might be a bit more gruff at first, but deep down he'd be protective of the little one. Amy would be over the moon and would constantly offer to babysit so she could play with the baby.
Their friends' reactions would vary. Tails would be enthusiastic and start thinking of all the ways he could help. He could create little gadgets for the baby, like a mini - sonic - speed - training - device when it gets older. Knuckles would be more of a protector. He'd see it as his duty to make sure the baby is safe, especially since Sonic is his friend. Rouge would be the fun auntie type. She'd bring stylish baby clothes and tell the baby all kinds of exciting stories from her travels. And the Chaotix might be a bit clumsy but well - intentioned in their attempts to interact with the baby.
Sonic would be devastated. He and Tails are like brothers. Sonic would likely go into a rage and vow to avenge Tails' death. He would immediately start hunting down whoever or whatever was responsible. Amy would be heartbroken as well. She would probably be the one to try to comfort Sonic while also being deeply sad herself. Knuckles would be angry and ready to fight alongside Sonic to seek justice for Tails.
Their friends would be really excited. Tails would probably be the first one to offer his help. He could use his mechanical skills to build baby - friendly gadgets. Knuckles would be a bit more gruff but still happy. He might offer to train the baby in self - defense when it grows up. Cream and Cheese would bring little presents for the baby, like cute toys or delicious Chao fruits.
Sonic usually feels a great deal of shock and confusion at first. He can't believe that his friends would turn on him. Then he might feel anger, especially if he discovers that they were misled or acting out of unjust reasons.
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.
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.
Some MHA characters might be flattered. For example, Midoriya would probably be really excited and take it as a sign of how much he's inspired people. He might even look for positive lessons in the fanfiction to improve himself.
Yang would likely have a big reaction. If the fanfiction shows her in a cool fight scene, she'd be all for it and might even show it off to her friends. But if it portrays her in a negative or weak way, she'd be really annoyed.