Master Fu would likely feel a great sense of responsibility. He might see Adrian's death as a sign that he failed in his duties as the guardian. Kagami could be deeply affected too, especially if she had feelings for Adrian. She might become more withdrawn or even vengeful towards whatever or whoever caused his death. The other Miraculous holders, if they exist in the story at that point, would be in a state of disbelief and would have to quickly figure out how to continue the fight against evil without Chat Noir.
Marinette (as Ladybug) would be devastated. She might isolate herself at first, blaming herself for not being able to prevent it. Alya would be very concerned for Marinette and try to comfort her, but also be in shock at the loss of Chat Noir. Nino would probably be heartbroken as well, since he was friends with Adrian. The other classmates might be sad and confused, and there could be a general sense of gloom over the school.
The villains in the story could have mixed reactions. Some might feel victorious at first, but then realize that without Chat Noir, Ladybug becomes a more unpredictable and dangerous opponent. Hawk Moth might even have a moment of regret, as Adrian was his son. He could either double - down on his evil plans out of grief or start to question his actions. The city of Paris itself would be in mourning, with people putting up tributes to Chat Noir and the general mood being one of sadness and fear for the future without their hero.
Perhaps in the fanfiction, Adrian's death could be a result of a self - sacrifice. He might give up his life to save Ladybug or Paris from a great danger. This would lead to a whole new set of challenges for Ladybug as she has to deal with the loss of her partner and also continue to protect the city without him. His death could also be a catalyst for a new hero to emerge, or for Ladybug to gain new powers out of her extreme emotions.
He could be shocked at first. I mean, he has been so close to Marinette all this time without realizing she was Ladybug. His reaction might include disbelief and then a quick acceptance as he starts to piece things together in his mind.
I really like 'Felix's Redemption'. In this fanfic, Felix starts off as a rather antagonistic character, but as the story progresses, his relationship with Adrian evolves. It's interesting to see how they come to understand each other better, especially in the context of the Miraculous Ladybug universe with all its magic and mystery.
Marinette's friends, like Alya, would be heartbroken. Alya, being Ladybug's biggest supporter, would probably feel a sense of loss and confusion. She might start to investigate Ladybug's death, trying to figure out what really happened. The other classmates would also be affected, with the mood at school becoming very somber.
One popular theme is family secrets. Given their family background in the Miraculous Ladybug world, fanfictions often explore the secrets that Felix and Adrian might be hiding from each other or from the rest of the world. For example, there could be secrets related to their parents' past or the true nature of their family business.
Master Fu might be a bit more cautious. He would see the potential risks not only to Ladybug but also to the Miraculous. He might try to find a way to transfer the Miraculous to someone else temporarily during her pregnancy to ensure its safety. But he would also understand Ladybug's determination and try to support her as best he can while still being concerned about the balance of the Miraculous world.
Mr. Schuester would be in shock. He saw Rachel as one of his star pupils and a driving force in the Glee club. He would struggle with the guilt of not being able to protect her. He would try to keep the club going as a way to honor her memory, but it would be very difficult for him. He might also start a scholarship fund in Rachel's name for future Glee club members.
Marinette (Ladybug) would probably be both overjoyed and terrified. She'd be happy to have a new life in her family but also worried about protecting her. Adrien (Chat Noir) would be super excited and very protective. He might even be a bit over - protective at times. Alya would be the supportive best friend, helping Marinette with baby stuff and giving her advice on how to balance motherhood and superheroing.
Ladybug would see Disneyland as a place full of positive energy. She would be cautious at first, always on the lookout for any signs of trouble. But as she explores, she'd start to enjoy the different shows and parades. Chat Noir would be like a big kid. He'd want to try every single ride and interact with all the costumed characters. He might even challenge some of the Disney villains to a friendly duel. And Marinette, well, she'd be busy taking mental notes for her future fashion creations, while also being in love with the whole Disney atmosphere.
Annabeth would be devastated. She and Percy had a deep connection. She might go into a state of shock initially and then be filled with rage towards the enemies. She could become more reckless in her attempts to avenge Percy.