A great 'TMNT Mikey hurt' fanfiction is 'Mikey's Painful Encounter'. In this story, Mikey is hurt by a mutagen - related accident. His brothers are desperate to find a cure, and the fic does a good job of showing their emotional turmoil. There are also some really interesting side characters in this fanfic that add depth to the story. Additionally, 'Hurt Mikey, Stronger Spirit' is a fanfic where Mikey endures a physical injury but his spirit remains unbroken, and it's inspiring to read how he overcomes his pain.
One possible scenario could be that Mikey gets hurt during a fight with the Foot Clan. Maybe he underestimated an opponent and got a nasty cut on his arm. His brothers would then rush to his side, with Donnie trying to patch him up as quickly as possible while Leo and Raph stand guard, ready to fend off any further attacks.
In a fanfiction, Mikey might get hurt while trying to protect his brothers. For example, if the Kraang were attacking and his brothers were in danger, Mikey could jump in front of a powerful blast meant for them. This would leave him seriously injured, with his brothers then having to take care of him and find a way to heal him.
It could also be due to some sort of accident in the lair. Maybe there was an experiment gone wrong by Donnie. Mikey is curious by nature and might have been poking around where he shouldn't have, getting caught in an explosion or a malfunctioning device.
One common plotline could be his brothers' reactions. They might go into overprotective mode. For example, Donnie would immediately start working on medical treatments while Raph gets super angry and wants to find out who or what caused the injury. Leo, on the other hand, would try to keep everyone calm and focused on getting Mikey better.
Well, a plotline might involve Mikey being abused by a human who discovers his mutant identity and tries to keep him captive and mistreat him. Mikey would have to use his wits and ninja skills to escape. Or perhaps in a more emotional sense, Mikey is abused by the public's negative perception of mutants. This causes him to question his place in the world and his relationship with his brothers. He might start to withdraw, and the other turtles would have to help him regain his confidence.
In many 'TMNT Mikey hurt' fanfictions, a common plot element is Mikey's own attitude towards his injury. Sometimes he tries to be brave and not show how much pain he's in to not worry his brothers. Another element is the search for a cure or solution. If he's poisoned, they'll look for an antidote. If it's a physical wound, they'll try to find medical supplies or a way to heal it. And there's usually a lot of brotherly bonding as they take care of Mikey.
One common plot element could be the other turtles rallying around Mikey. They might try to find a cure or take care of him. For example, Donnie could use his scientific knowledge to diagnose Mikey. Another element could be Mikey's own struggle with being sick. He might feel weak and frustrated that he can't do his normal activities. Also, there could be a threat that takes advantage of Mikey's weakened state, like an enemy planning an attack while he's down.
In a fanfiction, Mikey might get hurt during a mission to infiltrate a Kraang base. He could be detected by security systems and get zapped by some sort of electric defense mechanism. This would leave him weak and in pain. His brothers would need to carry him out of there and find a way to reverse the effects of the zap. They'd be desperate to get Mikey back to his normal, energetic self.
One popular 'Jayfeather hurt' fanfiction could be where he gets injured during a battle with a rogue group. In this fic, his fellow Clan mates have to rally around to protect him and find a way to heal his wounds. The author might focus on his internal struggle as he's forced to rely on others due to his injury.
There's 'When Bakugou Fell'. Here, he gets injured while training too hard. His pride won't let him accept help at first, but as his condition worsens, he has to rely on his classmates. It shows a different side of his character, the more human and less brash side.