Often in these fanfics, Chat Noir is injured while protecting someone. For example, he might jump in front of a civilian or Ladybug to take a hit. Then, he has to deal with the after - effects of the injury, like not being able to transform for a while or having to find a way to heal without revealing his secret identity. This can lead to some really interesting character development as he has to rely on others in ways he's not used to.
One common storyline could be Chat Noir getting injured during a battle with a powerful akuma. He might struggle to hide his injury from Ladybug while still trying to help her defeat the villain. Another could be that he gets injured because of some sort of betrayal within the superhero community, and has to deal with the physical and emotional pain.
In some Chat Noir injured fanfics, the injury is a result of his own recklessness. He might be overconfident in a fight and underestimate the enemy. His injury then becomes a lesson for him to grow as a superhero. Writers might explore how he reflects on his actions, how it affects his relationship with Ladybug and the other characters, and how he overcomes the physical limitations of the injury to become a better hero.
One common plotline is Ladybug having to take on more responsibility while Chat Noir is injured. She might have to fight akumas alone and also take care of Chat Noir at the same time.
One common theme is the idea of false accusations. In many of these fanfics, Chat Noir is wrongly accused of criminal acts, which leads to a lot of drama and his struggle to prove his innocence.
One common theme is the struggle between Chat Noir's normal self and the akumatized version. There's often a battle within him as he tries to fight the akuma's influence. Another theme is the reaction of Ladybug and other characters. They are usually shocked and have to figure out how to save their friend.
I'm not entirely sure as I haven't specifically studied 'chat noir sensitive fanfic', but it could potentially include themes like Chat Noir's internal struggles, his relationships with other characters in a more complex and emotional way, or perhaps how he copes with difficult situations in the Miraculous universe.
One common theme is heroism. Chat Noir and his patrol are usually depicted as heroes fighting against evil. Another theme is friendship, as they rely on each other in their missions.
Some writers show his recovery through the help of his friends. Marinette, for instance, might secretly bring him food and medicine as Ladybug or just as herself. His kwami, Plagg, could also play a big role in his recovery by giving him advice or using his powers in a unique way to speed up the healing process.
One common scenario could be a girl playfully teasing Chat Noir at a Parisian rooftop. Maybe she drops hints about his secret identity while batting her eyelashes. Another might be a girl using her charm to get Chat Noir to protect her during an akuma attack, all the while flirting shamelessly.
Chat Noir is often extremely helpful in fanfics. He uses his superpowers like cataclysm to protect the city and the people he cares about. For example, in many fanfics, he might save a civilian from a falling building by using his agility and acrobatic skills. His helpful nature also extends to his relationships, as he is always there to support Ladybug, whether it's in battles or in dealing with personal issues.
Another theme might be rescue or recovery. The fic could focus on how Chat Noir's friends or Ladybug in particular try to help him when he's in this state. It could also touch on themes of sacrifice, as perhaps he got in this state because of protecting someone. For example, he might have taken a powerful hit from an akuma to save Ladybug, and now he's lying limp, and the story delves into how she deals with that and tries to revive or heal him.
Friendship is also a big theme. Through these fics, their friendship deepens as Chat Noir comforts Marinette. It shows how they can rely on each other even outside of their superhero and civilian identities.