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 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.
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.
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.
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.
Leo would likely take charge immediately. He'd assess the situation and start giving orders on how to help Mikey. He'd be calm on the outside but worried on the inside.
Leo would probably take charge immediately. He'd be focused on getting Mikey to safety and finding a way to treat his injuries. He might be blaming himself a bit for not being there to protect Mikey better.
In this kind of fanfiction, the creators usually play with the characters' original traits. Karai, with her ninja skills and her own motives, could either be an ally or an adversary to Dark Mikey. For example, they might be forced to team up against a common enemy, and during that process, they start to understand each other better. It's all about exploring the uncharted territories of their personalities and the possible dynamics between them.
One great 'tmnt female Mikey fanfiction' is 'The Girl in Orange'. It really delves into the idea of a female Mikey having unique adventures. Another interesting one could be 'Female Mikey's Hidden Power' which shows her discovering new abilities. There's also 'Mikey: A Girl's Tale' that focuses on her relationships within the TMNT group.